Difference between revisions of "User:Tohline/SSC/Virial/PolytropesEmbedded/FirstEffortAgain"

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=Virial Equilibrium of Adiabatic Spheres=
=Virial Equilibrium of Adiabatic Spheres=
Highlights of the rather detailed discussion presented below have been [[User:Tohline/SSC/Virial/PolytropesSummary|summarized in an accompanying chapter]] of this H_Book.
Highlights of the rather detailed discussion presented below have been [[User:Tohline/SSC/Virial/PolytropesEmbedded/SecondEffortAgain#Virial_Equilibrium_of_Adiabatic_Spheres_.28Summary.29|summarized in an accompanying chapter]] of this H_Book.
{{LSU_HBook_header}}
{{LSU_HBook_header}}


Line 182: Line 182:
<div align="center">
<div align="center">
<math>
<math>
2C \chi_\mathrm{eq}^{-2}  + ~3 B\chi_\mathrm{eq}^{3 -3\gamma_g} -~3A\chi_\mathrm{eq}^{-1}  -~ 3D \chi_\mathrm{eq}^3 = 0 \, ,
2\mathcal{C} \chi_\mathrm{eq}^{-2}  + ~3 \mathcal{B}\chi_\mathrm{eq}^{3 -3\gamma_g} -~3\mathcal{A}\chi_\mathrm{eq}^{-1}   
-~ 3\mathcal{D} \chi_\mathrm{eq}^3 = 0 \, ,
</math>
</math>
</div>
</div>
Line 190: Line 191:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~A</math>
<math>~\mathcal{A}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 202: Line 203:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~B</math>
<math>~\mathcal{B}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 231: Line 232:
   </td>
   </td>
</tr>
</tr>
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~C</math>
<math>~\mathcal{C}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 247: Line 249:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~D</math>
<math>~\mathcal{D}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 263: Line 265:
(The [[User:Tohline/SphericallySymmetricConfigurations/Virial#Structural_Form_Factors|dimensionless structural form factors]], <math>~\mathfrak{f}_i,</math> that appear in these expressions are defined ''for isolated polytropes'' in our accompanying introductory discussion and are [[User:Tohline/SSC/Virial/Polytropes#Role_of_Structural_Form_Factors|discussed further, below]].)  Once the pressure exerted by the external medium (<math>~P_e</math>), and the configuration's mass (<math>~M_\mathrm{tot}</math>), angular momentum (<math>~J</math>), and specific entropy (via <math>~K</math>) have been specified, the values of all of the coefficients are known and <math>~\chi_\mathrm{eq}</math> can be determined.
(The [[User:Tohline/SphericallySymmetricConfigurations/Virial#Structural_Form_Factors|dimensionless structural form factors]], <math>~\mathfrak{f}_i,</math> that appear in these expressions are defined ''for isolated polytropes'' in our accompanying introductory discussion and are [[User:Tohline/SSC/Virial/Polytropes#Role_of_Structural_Form_Factors|discussed further, below]].)  Once the pressure exerted by the external medium (<math>~P_e</math>), and the configuration's mass (<math>~M_\mathrm{tot}</math>), angular momentum (<math>~J</math>), and specific entropy (via <math>~K</math>) have been specified, the values of all of the coefficients are known and <math>~\chi_\mathrm{eq}</math> can be determined.


==Isolated Nonrotating Adiabatic Configuration==
For a nonrotating configuration <math>~(C=J=0)</math> that is not influenced by the effects of a bounding external medium <math>~(D=P_e = 0)</math>, the statement of virial equilibrium is,
<div align="center">
<math>
3 B\chi_\mathrm{eq}^{3 -3\gamma_g} -~3A\chi_\mathrm{eq}^{-1}  = 0 \, .
</math>
</div>


Hence, one equilibrium state exists for each value of <math>~\gamma_g</math> and it occurs where,
<div align="center" id="ABratios">
<table border="1" cellpadding="10" align="center">
<tr><td align="left">


For later use, we note that after making the substitution, <math>~\gamma_g \rightarrow (n+1)/n</math>,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
Line 278: Line 276:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\chi_\mathrm{eq}^{4-3\gamma_g} = \biggl( \frac{R_\mathrm{eq}}{R_\mathrm{norm}} \biggr)^{4-3\gamma_g} </math>
<math>~\biggl( \frac{\mathcal{A}}{\mathcal{B}} \biggr)^n</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 284: Line 282:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~\biggl\{ 
\frac{A}{B} \, .
\frac{3}{20\pi} \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W
</math>
\biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)  \frac{1}{\mathfrak{f}_M} \biggr]^{-(n+1)/n}
\cdot \mathfrak{f}_A^{-1}
\biggr\}^n</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>


<div align="center" id="TwoPointsOfView">
<table border="1" width="100%" cellpadding="8">
<tr>
<tr>
  <th align="center" colspan="2">
   <td align="right">
Two Points of View
&nbsp;
  </th>
</tr>
 
<tr>
  <td align="center" colspan="1">
In terms of <math>~K</math> and <math>~M_\mathrm{limit} ~(= M_\mathrm{tot})</math>
  </td>
  <td align="center" colspan="1">
In terms of <math>~P_c</math> and <math>~M_\mathrm{limit} ~(= M_\mathrm{tot})</math>
  </td>
</tr>
 
<tr>
  <td align="center" colspan="1">
 
<table border="0" cellpadding="5" align="center">
 
<tr>
   <td align="right">
<math>~\chi_\mathrm{eq}^{4-3\gamma_g}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 322: Line 298:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~5^{-n}
\biggl\{  
\biggl( \frac{3}{4\pi} \biggr)^n \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^{2n}
\frac{1}{5} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W
\biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr) \frac{1}{\mathfrak{f}_M} \biggr]^{-(n+1)}
\biggr\}
\cdot \biggl( \frac{\mathfrak{f}_W}{\mathfrak{f}_A} \biggr)^{n}
</math>
</math>
   </td>
   </td>
Line 335: Line 311:
   </td>
   </td>
   <td align="center">
   <td align="center">
&nbsp;
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~\frac{1}{5^n} \biggl( \frac{4\pi}{3} \biggr)  \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)^{n-1}
\times
\cdot \frac{\mathfrak{f}_W^n}{\mathfrak{f}_A^n \mathfrak{f}_M^{n-1}} \, ;
\biggl\{
\frac{3}{4\pi}  
\biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr) \frac{1}{\mathfrak{f}_M} \biggr]_\mathrm{eq}^{-{\gamma_g}}
\cdot \frac{1}{\mathfrak{f}_A}
\biggr\}
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
and,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\Rightarrow~~~R_\mathrm{eq}^{4-3\gamma_g}</math>
<math>~\frac{\mathcal{B}^{4n}}{\mathcal{A}^{3(n+1)}}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 357: Line 333:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~\biggl\{
\frac{4\pi}{3\cdot 5}  
\frac{1}{5} \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W \biggr\}^{-3(n+1)}
\biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr) \frac{1}{\mathfrak{f}_M} \biggr]_\mathrm{eq}^{2-{\gamma_g}}
\biggl\{ \frac{4\pi}{3}
\cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A} \biggl[
\biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)  \frac{1}{\mathfrak{f}_M} \biggr]^{(n+1)/n}
\frac{GM_\mathrm{tot}^{2-\gamma_g}}{K} \biggr]
\cdot \mathfrak{f}_A
</math>
\biggr\}^{4n}</math>
   </td>
   </td>
</tr>
</tr>
Line 368: Line 344:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\Rightarrow ~~\frac{KR_\mathrm{eq}^{4-3\gamma_g}}{GM_\mathrm{limit}^{2-\gamma_g}}</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 374: Line 350:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~
\frac{1}{5} \biggl( \frac{4\pi}{3} \biggr)^{\gamma_g-1} \frac{\mathfrak{f}_W}{\mathfrak{f}_A \mathfrak{f}_M^{2-\gamma_g}}
5^{3(n+1)}  \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^{-6(n+1)}  
\biggl( \frac{4\pi}{3} \biggr)^{4n-4(n+1)}
\biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)  \frac{1}{\mathfrak{f}_M} \biggr]^{4(n+1)} \cdot\frac{\mathfrak{f}_A^{4n}}{\mathfrak{f}_W^{3(n+1)}}
</math>
</math>
   </td>
   </td>
</tr>
</tr>
<tr>
<tr>
   <td align="center" colspan="3">
  <td align="right">
&#8212; &#8212; &#8212; &#8212; &#8212; &#8212; &nbsp; &nbsp; or,
&nbsp;
inverted and setting <math>~\gamma_g = 1 + 1/n</math> &nbsp; &nbsp; &#8212; &#8212; &#8212; &#8212; &#8212; &#8212;
  </td>
   <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~  
5^{3(n+1)} \biggl( \frac{3}{4\pi} \biggr)^{4} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2(n+1)}
\cdot\frac{\mathfrak{f}_A^{4n} \mathfrak{f}_M^{2(n+1)} }{\mathfrak{f}_W^{3(n+1)}}
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>


<tr>
</td></tr>
  <td align="center" colspan="3">
</table>
<math>~
</div>
4\pi \biggl( \frac{G}{K} \biggr)^n M_\mathrm{limit}^{n-1} R_\mathrm{eq}^{3-n}
 
=
==Isolated Nonrotating Adiabatic Configuration==
\biggl( \frac{5 \mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} \biggr)^n \frac{3}{\mathfrak{f}_M}
For a nonrotating configuration <math>~(C=J=0)</math> that is not influenced by the effects of a bounding external medium <math>~(D=P_e = 0)</math>, the statement of virial equilibrium is,
<div align="center">
<math>
3 B\chi_\mathrm{eq}^{3 -3\gamma_g} -~3A\chi_\mathrm{eq}^{-1} = 0 \, .
</math>
</math>
  </td>
</div>
</tr>


</table>
Hence, one equilibrium state exists for each value of <math>~\gamma_g</math> and it occurs where,
 
  </td>
  <td align="center" colspan="1">


<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\chi_\mathrm{eq}^{4-3\gamma_g}</math>
<math>~\chi_\mathrm{eq}^{4-3\gamma_g} = \biggl( \frac{R_\mathrm{eq}}{R_\mathrm{norm}} \biggr)^{4-3\gamma_g} </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 411: Line 400:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>  
<math>
\biggl\{
\frac{A}{B} \, .
\frac{1}{5} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W
\biggr\}
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>


<div align="center" id="TwoPointsOfView">
<table border="1" width="100%" cellpadding="8">
<tr>
<tr>
   <td align="right">
  <th align="center" colspan="2">
&nbsp;
Two Points of View
  </th>
</tr>
 
<tr>
  <td align="center" colspan="1">
In terms of <math>~K</math> and <math>~M_\mathrm{limit} ~(= M_\mathrm{tot})</math>
  </td>
  <td align="center" colspan="1">
In terms of <math>~P_c</math> and <math>~M_\mathrm{limit} ~(= M_\mathrm{tot})</math>
  </td>
</tr>
 
<tr>
  <td align="center" colspan="1">
 
<table border="0" cellpadding="5" align="center">
 
<tr>
   <td align="right">
<math>~\chi_\mathrm{eq}^{4-3\gamma_g}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
&nbsp;
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>
\times
\biggl\{  
\biggl\{  
\frac{3} {4\pi}
\frac{1}{5} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W
\biggl[ \biggl( \frac{P_\mathrm{norm}}{P_c} \biggr)\chi^{-3\gamma} \biggr]_\mathrm{eq}
\cdot \frac{1}{\mathfrak{f}_A}
\biggr\}
\biggr\}
</math>
</math>
Line 440: Line 448:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\Rightarrow~~~\chi_\mathrm{eq}^{4}</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
&nbsp;
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>  
<math>
\frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2
\times
\biggl( \frac{P_\mathrm{norm}}{P_c} \biggr)
\biggl\{
\cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \cdot \mathfrak{f}_M^2}
\frac{3}{4\pi}
\biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr) \frac{1}{\mathfrak{f}_M} \biggr]_\mathrm{eq}^{-{\gamma_g}}
\cdot \frac{1}{\mathfrak{f}_A}
\biggr\}
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\Rightarrow~~~\frac{P_c R_\mathrm{eq}^{4}}{P_\mathrm{norm} R_\mathrm{norm}^4} \biggl( \frac{M_\mathrm{tot}}{M_\mathrm{limit}} \biggr)^{2}</math>
<math>~\Rightarrow~~~R_\mathrm{eq}^{4-3\gamma_g}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 465: Line 473:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>  
<math>
\frac{3}{20\pi} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \cdot \mathfrak{f}_M^2}
\frac{4\pi}{3\cdot 5}
\biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)  \frac{1}{\mathfrak{f}_M} \biggr]_\mathrm{eq}^{2-{\gamma_g}}
\cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A} \biggl[
\frac{GM_\mathrm{tot}^{2-\gamma_g}}{K} \biggr]
</math>
</math>
   </td>
   </td>
Line 473: Line 484:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\Rightarrow~~~\frac{P_c R_\mathrm{eq}^{4}}{G M_\mathrm{limit}^2} </math>
<math>\Rightarrow ~~\frac{KR_\mathrm{eq}^{4-3\gamma_g}}{GM_\mathrm{limit}^{2-\gamma_g}}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 479: Line 490:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>  
<math>
\frac{3}{20\pi} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \cdot \mathfrak{f}_M^2}
\frac{1}{5} \biggl( \frac{4\pi}{3} \biggr)^{\gamma_g-1} \frac{\mathfrak{f}_W}{\mathfrak{f}_A \mathfrak{f}_M^{2-\gamma_g}}
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
<tr>
 
  <td align="center" colspan="3">
&#8212; &#8212; &#8212; &#8212; &#8212; &#8212; &nbsp; &nbsp; or,
inverted and setting <math>~\gamma_g = 1 + 1/n</math> &nbsp; &nbsp; &#8212; &#8212; &#8212; &#8212; &#8212; &#8212;
   </td>
   </td>
</tr>
</tr>
</table>
</div>


According to the solution shown in the left-hand column, for fluid with a given specify entropy content, the equilibrium mass-radius relationship for adiabatic configurations is,
<tr>
<div align="center">
  <td align="center" colspan="3">
<math>
<math>~
M_\mathrm{tot}^{(\gamma_g - 2)} \propto R_\mathrm{eq}^{(3\gamma_g -4)} \, .
4\pi \biggl( \frac{G}{K} \biggr)^n M_\mathrm{limit}^{n-1} R_\mathrm{eq}^{3-n}
=
\biggl( \frac{5 \mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} \biggr)^n \frac{3}{\mathfrak{f}_M}
</math>
</math>
</div>
  </td>
We see that, for <math>~\gamma_g=2</math>, the equilibrium radius depends only on the specific entropy of the gas and is independent of the configuration's mass.  Conversely, for <math>~\gamma_g = 4/3</math>, the mass of the configuration is independent of the radius.  For <math>~\gamma_g > 2</math> or <math>~\gamma_g < 4/3</math>, configurations with larger mass (but the same specific entropy) have larger equilibrium radii.  However, for <math>~\gamma_g</math> in the range, <math>~2 > \gamma_g > 4/3</math>, configurations with larger mass have smaller equilibrium radii.  (Note that the related result for [[User:Tohline/SSC/Virial/Isothermal#Virial_Equilibrium_of_Isothermal_Spheres|isothermal configurations]] can be obtained by setting <math>~\gamma_g = 1</math> in this adiabatic solution, because <math>~K = c_s^2</math> when  <math>~\gamma_g = 1</math>.)
</tr>
 
</table>
 
  </td>
  <td align="center" colspan="1">


==Role of Structural Form Factors==
When employing a virial analysis to determine the radius of an equilibrium configuration, it is customary to set the structural form factors, <math>~\mathfrak{f}_M</math>, <math>~\mathfrak{f}_W</math> and <math>~\mathfrak{f}_A</math>, to unity and accept that the expression derived for <math>~R_\mathrm{eq}</math> is an estimate of the configuration's radius that is good to within a factor of order unity.  As has been demonstrated in our [[User:Tohline/SSC/VirialEquilibrium/UniformDensity#Comparison_with_Detailed_Force-Balance_Model|related discussion of the equilibrium of uniform-density spheres]], these form factors can be evaluated if/when the internal structural profile of an equilibrium configuration is known from a complementary detailed force-balance analysis.  In the case being discussed here of isolated, spherical polytropes, [[User:Tohline/SSC/Structure/Polytropes#Lane-Emden_Equation|solutions to the]],
<div align="center">
<span id="LaneEmdenEquation"><font color="#770000">'''Lane-Emden Equation'''</font></span>
<br />
{{User:Tohline/Math/EQ_SSLaneEmden01}}
</div>
can provide the desired internal structural information.  Here we draw on [[User:Tohline/Appendix/References|Chandrasekhar's [C67]]] discussion of the structure of spherical polytropes to show precisely how our structural form factors can be expressed in terms of the Lane-Emden function, <math>~\Theta_H</math>, dimensionless radial coordinate, <math>~\xi</math>, and the function derivative, <math>~\Theta^' = d\Theta_H/d\xi</math>.
===Mass===
We note, first, that [[User:Tohline/Appendix/References|Chandrasekhar [C67]]] &#8212; see his Equation (78) on p. 99 &#8212; presents the following expression for the mean-to-central density ratio:
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\frac{\bar\rho}{\rho_c}</math>
<math>~\chi_\mathrm{eq}^{4-3\gamma_g}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 520: Line 527:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\xi_1} \, ,</math>
<math>  
\biggl\{
\frac{1}{5} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W
\biggr\}
</math>
   </td>
   </td>
</tr>
</tr>
</table>
 
</div>
<tr>
where the notation at the bottom of the closing square bracket means that everything inside the square brackets should be, "evaluated at the surface of the configuration," that is, at the radial location, <math>~\xi_1</math>, where the Lane-Emden function, <math>~\Theta_H(\xi)</math>, first goes to zero.  But, as we pointed out when [[User:Tohline/SphericallySymmetricConfigurations/Virial#Structural_Form_Factors|defining the structural form factors]], the form factor associated with the configuration mass, <math>~\mathfrak{f}_M</math>, is equivalent to the mean-to-central density ratio.  We conclude, therefore, that,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
   <td align="right">
   <td align="right">
<math>~\mathfrak{f}_M</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
&nbsp;
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\xi_1} \, .</math>
<math>
\times
\biggl\{
\frac{3} {4\pi}
\biggl[ \biggl( \frac{P_\mathrm{norm}}{P_c} \biggr)\chi^{-3\gamma} \biggr]_\mathrm{eq}
\cdot \frac{1}{\mathfrak{f}_A}
\biggr\}
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>


===Gravitational Potential Energy===
Second, we note that [[User:Tohline/Appendix/References|Chandrasekhar's [C67]]] expression for the gravitational potential energy &#8212; see his Equation (90), p. 101 &#8212; is,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~-W</math>
<math>~\Rightarrow~~~\chi_\mathrm{eq}^{4}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 555: Line 562:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{3}{5-n} \biggl( \frac{GM^2}{R} \biggr) \, ,</math>
<math>  
\frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2
\biggl( \frac{P_\mathrm{norm}}{P_c} \biggr)
\cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \cdot \mathfrak{f}_M^2}
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
 
whereas our analogous expression is,
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~-W_\mathrm{grav}</math>
<math>~\Rightarrow~~~\frac{P_c R_\mathrm{eq}^{4}}{P_\mathrm{norm} R_\mathrm{norm}^4} \biggl( \frac{M_\mathrm{tot}}{M_\mathrm{limit}} \biggr)^{2}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 571: Line 581:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{3}{5} \biggl( \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}} \biggr) \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \, .</math>
<math>  
\frac{3}{20\pi} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \cdot \mathfrak{f}_M^2}
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
We conclude, therefore, that,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} </math>
<math>~\Rightarrow~~~\frac{P_c R_\mathrm{eq}^{4}}{G M_\mathrm{limit}^2} </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 588: Line 595:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{5}{5-n} </math>
<math>  
\frac{3}{20\pi} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \cdot \mathfrak{f}_M^2}
</math>
   </td>
   </td>
</tr>
</tr>
</table>


<tr>
  <td align="right">
<math>\Rightarrow ~~~~\mathfrak{f}_W </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\frac{3^2\cdot 5}{5-n} \biggl[ \frac{\Theta^'}{\xi} \biggr]^2_{\xi_1} \, .</math>
   </td>
   </td>
</tr>
</tr>
Line 606: Line 607:
</div>
</div>


===Mass-Radius Relationship===
According to the solution shown in the left-hand column, for fluid with a given specify entropy content, the equilibrium mass-radius relationship for adiabatic configurations is,
Third, [[User:Tohline/Appendix/References|Chandrasekhar [C67]]] shows &#8212; see his Equation (72), p. 98 &#8212; that the general mass-radius relationship for isolated spherical polytropes is,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~GM^{(n-1)/n} R^{(3-n)/n}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
<math>
~\frac{(n+1)K}{(4\pi)^{1/n}} \biggl[ - \xi^{(n+1)/(n-1)} \frac{d\Theta_H}{d\xi} \biggr]^{(n-1)/n}_{\xi=\xi_1} \, ,
M_\mathrm{tot}^{(\gamma_g - 2)} \propto R_\mathrm{eq}^{(3\gamma_g -4)} \, .
</math>
</math>
  </td>
</tr>
</table>
</div>
</div>
which we choose to rewrite as,
We see that, for <math>~\gamma_g=2</math>, the equilibrium radius depends only on the specific entropy of the gas and is independent of the configuration's mass.  Conversely, for <math>~\gamma_g = 4/3</math>, the mass of the configuration is independent of the radius.  For <math>~\gamma_g > 2</math> or <math>~\gamma_g <  4/3</math>, configurations with larger mass (but the same specific entropy) have larger equilibrium radii.  However, for <math>~\gamma_g</math> in the range, <math>~2 > \gamma_g > 4/3</math>, configurations with larger mass have smaller equilibrium radii.  (Note that the related result for [[User:Tohline/SSC/Virial/Isothermal#Virial_Equilibrium_of_Isothermal_Spheres|isothermal configurations]] can be obtained by setting <math>~\gamma_g = 1</math> in this adiabatic solution, because <math>~K = c_s^2</math> when  <math>~\gamma_g = 1</math>.)
 
==Role of Structural Form Factors==
When employing a virial analysis to determine the radius of an equilibrium configuration, it is customary to set the structural form factors, <math>~\mathfrak{f}_M</math>, <math>~\mathfrak{f}_W</math> and <math>~\mathfrak{f}_A</math>, to unity and accept that the expression derived for <math>~R_\mathrm{eq}</math> is an estimate of the configuration's radius that is good to within a factor of order unity.  As has been demonstrated in our [[User:Tohline/SSC/VirialEquilibrium/UniformDensity#Comparison_with_Detailed_Force-Balance_Model|related discussion of the equilibrium of uniform-density spheres]], these form factors can be evaluated if/when the internal structural profile of an equilibrium configuration is known from a complementary detailed force-balance analysis.  In the case being discussed here of isolated, spherical polytropes, [[User:Tohline/SSC/Structure/Polytropes#Lane-Emden_Equation|solutions to the]],
<div align="center">
<span id="LaneEmdenEquation"><font color="#770000">'''Lane-Emden Equation'''</font></span>
<br />
{{User:Tohline/Math/EQ_SSLaneEmden01}}
</div>
can provide the desired internal structural information.  Here we draw on [[User:Tohline/Appendix/References|Chandrasekhar's [C67]]] discussion of the structure of spherical polytropes to show precisely how our structural form factors can be expressed in terms of the Lane-Emden function, <math>~\Theta_H</math>, dimensionless radial coordinate, <math>~\xi</math>, and the function derivative, <math>~\Theta^' = d\Theta_H/d\xi</math>.
===Mass===
We note, first, that [[User:Tohline/Appendix/References|Chandrasekhar [C67]]] &#8212; see his Equation (78) on p. 99 &#8212; presents the following expression for the mean-to-central density ratio:
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~4\pi \biggl( \frac{G}{K}\biggr)^n M^{(n-1)} R^{(3-n)}</math>
<math>~\frac{\bar\rho}{\rho_c}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 637: Line 636:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\xi_1} \, ,</math>
~(n+1)^n\biggl[ \xi^{(n+1)} (-\Theta^')^{(n-1)}\biggr]_{\xi=\xi_1}  
</math>
   </td>
   </td>
</tr>
</tr>
 
</table>
</div>
where the notation at the bottom of the closing square bracket means that everything inside the square brackets should be, "evaluated at the surface of the configuration," that is, at the radial location, <math>~\xi_1</math>, where the Lane-Emden function, <math>~\Theta_H(\xi)</math>, first goes to zero.  But, as we pointed out when [[User:Tohline/SphericallySymmetricConfigurations/Virial#Structural_Form_Factors|defining the structural form factors]], the form factor associated with the configuration mass, <math>~\mathfrak{f}_M</math>, is equivalent to the mean-to-central density ratio.  We conclude, therefore, that,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\mathfrak{f}_M</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 651: Line 652:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\xi_1} \, .</math>
- \biggl( \frac{\xi}{\Theta^'} \biggr)_{\xi=\xi_1} \biggl[ (n+1) \xi ~(-\Theta^') \biggr]^n_{\xi=\xi_1} \, .
</math>
   </td>
   </td>
</tr>
</tr>
Line 659: Line 658:
</div>
</div>


By comparison, the expression for the equilibrium radius that has been derived, above, from an analysis of extrema in the free energy function &#8212; specifically, see the last expression in the left-hand column of the [[User:Tohline/SSC/Virial/Polytropes#TwoPointsOfView|table titled "Two Points of View"]] &#8212; we obtain,
 
===Gravitational Potential Energy===
Second, we note that [[User:Tohline/Appendix/References|Chandrasekhar's [C67]]] expression for the gravitational potential energy &#8212; see his Equation (90), p. 101 &#8212; is,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~4\pi \biggl( \frac{G}{K}\biggr)^n M^{(n-1)} R_\mathrm{eq}^{(3-n)}</math>
<math>~-W</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 670: Line 671:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~\frac{3}{5-n} \biggl( \frac{GM^2}{R} \biggr) \, ,</math>
~\frac{3}{\mathfrak{f}_M} \biggl( \frac{5\mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} \biggr)^n \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
Hence, it appears as though, quite generally,
whereas our analogous expression is,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~ \frac{1}{\mathfrak{f}_M} \biggl( \frac{5\mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} \biggr)^n </math>
<math>~-W_\mathrm{grav}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 688: Line 687:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~\frac{3}{5} \biggl( \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}} \biggr) \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \, .</math>
- \biggl( \frac{\xi}{3\Theta^'} \biggr)_{\xi=\xi_1} \biggl[ (n+1) \xi ~(-\Theta^') \biggr]^n_{\xi=\xi_1} \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
Or, taking into account the expressions for <math>~\mathfrak{f}_M</math> and <math>~\mathfrak{f}_W</math> that have just been uncovered, we conclude that,
We conclude, therefore, that,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
Line 701: Line 698:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~ \frac{5\mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} </math>
<math>~\frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 707: Line 704:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~\frac{5}{5-n} </math>
\biggl[ (n+1) \xi ~(-\Theta^') \biggr]_{\xi=\xi_1}
</math>
   </td>
   </td>
</tr>
</tr>
Line 715: Line 710:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\Rightarrow ~~~~ \frac{\mathfrak{f}_A}{\mathfrak{f}_W</math>
<math>\Rightarrow ~~~~\mathfrak{f}_W </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 721: Line 716:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~\frac{3^2\cdot 5}{5-n} \biggl[ \frac{\Theta^'}{\xi} \biggr]^2_{\xi_1} \, .</math>
\frac{(n+1) }{3\cdot 5} ~\xi_1^2 \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>


===Mass-Radius Relationship===
Third, [[User:Tohline/Appendix/References|Chandrasekhar [C67]]] shows &#8212; see his Equation (72), p. 98 &#8212; that the general mass-radius relationship for isolated spherical polytropes is,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\Rightarrow ~~~~ \mathfrak{f}_A  </math>
<math>~GM^{(n-1)/n} R^{(3-n)/n}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 736: Line 735:
   <td align="left">
   <td align="left">
<math>
<math>
\frac{(n+1) }{3\cdot 5} ~\xi_1^2 \biggl\{ \frac{3^2\cdot 5}{5-n} \biggl[ \frac{\Theta^'}{\xi} \biggr]^2_{\xi_1} \biggr\}\, .
~\frac{(n+1)K}{(4\pi)^{1/n}} \biggl[ - \xi^{(n+1)/(n-1)} \frac{d\Theta_H}{d\xi} \biggr]^{(n-1)/n}_{\xi=\xi_1} \, ,
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
which we choose to rewrite as,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~4\pi \biggl( \frac{G}{K}\biggr)^n M^{(n-1)} R^{(3-n)}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 750: Line 754:
   <td align="left">
   <td align="left">
<math>
<math>
\frac{3(n+1) }{(5-n)} ~\biggl[ \Theta^' \biggr]^2_{\xi_1} \, .
~(n+1)^n\biggl[ \xi^{(n+1)} (-\Theta^')^{(n-1)}\biggr]_{\xi=\xi_1}  
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>


===Central and Mean Pressure===
It is also worth pointing out that [[User:Tohline/Appendix/References|Chandrasekhar [C67]]] &#8212; see his Equations (80) &amp; (81), p. 99 &#8212; introduces a dimensionless structural form factor, <math>~W_n</math>, for the central pressure via the expression,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~P_c</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 769: Line 767:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~W_n \biggl( \frac{GM^2}{R^4} \biggr) \, ,</math>
<math>
- \biggl( \frac{\xi}{\Theta^'} \biggr)_{\xi=\xi_1} \biggl[ (n+1) \xi ~(-\Theta^') \biggr]^n_{\xi=\xi_1} \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
and demonstrates that,
 
By comparison, the expression for the equilibrium radius that has been derived, above, from an analysis of extrema in the free energy function &#8212; specifically, see the last expression in the left-hand column of the [[User:Tohline/SSC/Virial/Polytropes#TwoPointsOfView|table titled "Two Points of View"]] &#8212; we obtain,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\frac{1}{W_n}</math>
<math>~4\pi \biggl( \frac{G}{K}\biggr)^n M^{(n-1)} R_\mathrm{eq}^{(3-n)}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~\equiv</math>
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~4\pi (n+1) \biggl[ \Theta^' \biggr]^2_{\xi_1} \, .</math>
<math>
~\frac{3}{\mathfrak{f}_M} \biggl( \frac{5\mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} \biggr)^n \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
It is therefore clear that a spherical polytrope's central pressure is expressible in terms of our structural form factor, <math>~\mathfrak{f}_A</math>, as,
Hence, it appears as though, quite generally,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~P_c</math>
<math>~ \frac{1}{\mathfrak{f}_M} \biggl( \frac{5\mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} \biggr)^n </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 801: Line 804:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{3}{4\pi (5-n)} \biggl( \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}^4} \biggr) \frac{1}{\mathfrak{f}_A} \, .</math>
<math>
- \biggl( \frac{\xi}{3\Theta^'} \biggr)_{\xi=\xi_1} \biggl[ (n+1) \xi ~(-\Theta^') \biggr]^n_{\xi=\xi_1} \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
 
Or, taking into account the expressions for <math>~\mathfrak{f}_M</math> and <math>~\mathfrak{f}_W</math> that have just been uncovered, we conclude that,
Looking back at our [[User:Tohline/SphericallySymmetricConfigurations/Virial#FormFactors|original definition of the structural form factors]], we note that,
<div align="center">
<div align="center">
<math>\mathfrak{f}_A = \biggl( \frac{\bar{P}}{P_c} \biggr)_\mathrm{eq} \, .</math>
<table border="0" cellpadding="5" align="center">
</div>
Hence, this last equilibrium relation can be rewritten as,
<div align="center">
<math> \frac{\bar{P} R_\mathrm{eq}^4}{GM_\mathrm{tot}^2} = \frac{3}{4\pi (5-n)} \, .</math>
</div>
 
===Alternate Derivation of Gravitational Potential Energy===
 
<!-- BEGINNING OF DELETION:  The following subsubsection is redundant, now that the "Two Points of View" table has been included.


====Central Pressure====
As is pointed out, above, in our [[User:Tohline/SSC/Virial/Polytropes#Mass-Radius_Relationship|discussion of the mass-radius relationship]], the expression for the equilibrium radius that has been derived from our analysis of extrema in the free energy function can be written as,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~4\pi \biggl( \frac{G}{K}\biggr)^n M^{(n-1)} R_\mathrm{eq}^{(3-n)}</math>
<math>~ \frac{5\mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 833: Line 824:
   <td align="left">
   <td align="left">
<math>
<math>
~\frac{3}{\mathfrak{f}_M} \biggl( \frac{5\mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} \biggr)^n \, .
\biggl[ (n+1) \xi ~(-\Theta^') \biggr]_{\xi=\xi_1}
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
Via the polytropic equation of state, we can relate <math>~K</math> to the central pressure as follows:
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~P_c</math>
<math>\Rightarrow ~~~~ \frac{\mathfrak{f}_A}{\mathfrak{f}_W}  </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 852: Line 838:
   <td align="left">
   <td align="left">
<math>
<math>
~K \rho_c^{1+1/n} = K \bar\rho^{1+1/n} \biggl( \frac{\rho_c}{\bar\rho} \biggr)^{1+1/n}
\frac{(n+1) }{3\cdot 5} ~\xi_1^2 \, .
= K \biggl[ \frac{3M_\mathrm{tot}}{4\pi R_\mathrm{eq}^3} \biggr]^{(n+1)/n} \biggl( \frac{1}{\mathfrak{f}_M} \biggr)^{(n+1)/n}
</math>
</math>
   </td>
   </td>
Line 860: Line 845:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\Rightarrow ~~~~ K^{n}</math>
<math>\Rightarrow ~~~~ \mathfrak{f}_A  </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 867: Line 852:
   <td align="left">
   <td align="left">
<math>
<math>
P_c^{n} \biggl[ \frac{4\pi R_\mathrm{eq}^3}{3M_\mathrm{tot}} \biggr]^{(n+1)} \mathfrak{f}_M^{(n+1)} \, .
\frac{(n+1) }{3\cdot 5} ~\xi_1^2 \biggl\{ \frac{3^2\cdot 5}{5-n} \biggl[ \frac{\Theta^'}{\xi} \biggr]^2_{\xi_1} \biggr\}\, .
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
Hence, in the mass-radius relationship we can replace <math>~K</math> with this expression to obtain,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~4\pi \biggl( \frac{G}{P_c}\biggr)^n M^{(n-1)} R_\mathrm{eq}^{(3-n)}
&nbsp;
\biggl[ \frac{3M_\mathrm{tot}}{4\pi R_\mathrm{eq}^3} \biggr]^{(n+1)}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 887: Line 866:
   <td align="left">
   <td align="left">
<math>
<math>
~3 \biggl( \frac{5\mathfrak{f}_A \mathfrak{f}_M^2}{\mathfrak{f}_W} \biggr)^n
\frac{3(n+1) }{(5-n)} ~\biggl[ \Theta^' \biggr]^2_{\xi_1} \, .
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>


===Central and Mean Pressure===
It is also worth pointing out that [[User:Tohline/Appendix/References|Chandrasekhar [C67]]] &#8212; see his Equations (80) &amp; (81), p. 99 &#8212; introduces a dimensionless structural form factor, <math>~W_n</math>, for the central pressure via the expression,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\Rightarrow ~~~~ \biggl( \frac{G M_\mathrm{tot}^2}{P_c R_\mathrm{eq}^4}\biggr)^n
<math>~P_c</math>
\biggl( \frac{3}{4\pi } \biggr)^{n}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 901: Line 885:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~W_n \biggl( \frac{GM^2}{R^4} \biggr) \, ,</math>
~\biggl( \frac{5\mathfrak{f}_A \mathfrak{f}_M^2}{\mathfrak{f}_W} \biggr)^n
</math>
  </td>
</tr>
 
<tr>
  <td align="right" colspan="3">
<math>
\Rightarrow ~~~~ P_c = \frac{3 }{20\pi }\biggl( \frac{G M_\mathrm{tot}^2}{R_\mathrm{eq}^4} \biggr)
\cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \mathfrak{f}_M^2}  \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
Now, from our above [[User:Tohline/SSC/Virial/Polytropes#Gravitational_Potential_Energy|examination of the expression for the gravitational potential energy]], we know that,
and demonstrates that,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>
<math>~\frac{1}{W_n}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
<math>~\equiv</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{5}{5-n} \, .</math>
<math>~4\pi (n+1) \biggl[ \Theta^' \biggr]^2_{\xi_1} \, .</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
Hence, our expression for the central pressure becomes,
It is therefore clear that a spherical polytrope's central pressure is expressible in terms of our structural form factor, <math>~\mathfrak{f}_A</math>, as,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right" colspan="3">
<math>
~P_c = \frac{3 }{4\pi (5-n)}\biggl( \frac{G M_\mathrm{tot}^2}{R_\mathrm{eq}^4} \biggr)
\cdot \frac{1}{\mathfrak{f}_A }  \, .
</math>
  </td>
</tr>
</table>
</div>
As it should, this precisely matches [[User:Tohline/SSC/Virial/Polytropes#Central_Pressure|the expression that we derived, above]], starting from [[User:Tohline/Appendix/References|Chandrasekhar's [C67]]] presentation.
====Gravitational Potential Energy====
END OF DELETION  -->
As has been [[User:Tohline/SphericallySymmetricConfigurations/Virial#AlternateGravPotEnergy|discussed elsewhere]], we have learned from [[User:Tohline/Appendix/References|Chandrasekhar's discussion of polytropic spheres [C67]]] &#8212; see his Equation (16), p. 64 &#8212; that if a spherically symmetric system is in hydrostatic balance, the total gravitational potential energy can be obtained from the following integral:
<div align="center">
<table border="0" cellpadding="5">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~W_\mathrm{grav}</math>
<math>~P_c</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 964: Line 917:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ + \frac{1}{2} \int_0^R \Phi(r) dm \, .</math>
<math>~\frac{3}{4\pi (5-n)} \biggl( \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}^4} \biggr) \frac{1}{\mathfrak{f}_A} \, .</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
Using "[[User:Tohline/SphericallySymmetricConfigurations/SolutionStrategies#Technique_3|technique #3]]" to solve the differential equation that governs the statement of hydrostatic balance, we know that in any polytropic sphere, <math>~\Phi(r)</math> is related to the configuration's radial enthalpy profile, <math>~H(r)</math>, via the algebraic expression,
 
Looking back at our [[User:Tohline/SphericallySymmetricConfigurations/Virial#FormFactors|original definition of the structural form factors]], we note that,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<math>\mathfrak{f}_A = \biggl( \frac{\bar{P}}{P_c} \biggr)_\mathrm{eq} \, .</math>
</div>
Hence, this last equilibrium relation can be rewritten as,
<div align="center">
<math> \frac{\bar{P} R_\mathrm{eq}^4}{GM_\mathrm{tot}^2} = \frac{3}{4\pi (5-n)} \, .</math>
</div>
 
===Alternate Derivation of Gravitational Potential Energy===
 
<!-- BEGINNING OF DELETION:  The following subsubsection is redundant, now that the "Two Points of View" table has been included.
 
====Central Pressure====
As is pointed out, above, in our [[User:Tohline/SSC/Virial/Polytropes#Mass-Radius_Relationship|discussion of the mass-radius relationship]], the expression for the equilibrium radius that has been derived from our analysis of extrema in the free energy function can be written as,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\Phi(r) + H(r)</math>
<math>~4\pi \biggl( \frac{G}{K}\biggr)^n M^{(n-1)} R_\mathrm{eq}^{(3-n)}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 980: Line 948:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~C_B \, ,</math>
<math>
~\frac{3}{\mathfrak{f}_M} \biggl( \frac{5\mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} \biggr)^n \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
where, <math>~C_B</math>, is an integration constant.  At the surface of the equilibrium configuration, <math>~H = 0</math> and <math>~\Phi = - GM_\mathrm{tot}/R_\mathrm{eq}</math>, so the integration constant is,
Via the polytropic equation of state, we can relate <math>~K</math> to the central pressure as follows:
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~C_B</math>
<math>~P_c</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 996: Line 967:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~- \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \, ,</math>
<math>
~K \rho_c^{1+1/n} = K \bar\rho^{1+1/n} \biggl( \frac{\rho_c}{\bar\rho} \biggr)^{1+1/n}
= K \biggl[ \frac{3M_\mathrm{tot}}{4\pi R_\mathrm{eq}^3} \biggr]^{(n+1)/n} \biggl( \frac{1}{\mathfrak{f}_M} \biggr)^{(n+1)/n}
</math>
   </td>
   </td>
</tr>
</tr>
</table>
 
</div>
which implies,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\Phi(r) </math>
<math>\Rightarrow ~~~~ K^{n}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,012: Line 982:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ - H(r) - \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \, .</math>
<math>
P_c^{n} \biggl[ \frac{4\pi R_\mathrm{eq}^3}{3M_\mathrm{tot}} \biggr]^{(n+1)} \mathfrak{f}_M^{(n+1)} \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
Now, from [[User:Tohline/SR#Barotropic_Structure|our general discussion of barotropic relations]], we can write,
Hence, in the mass-radius relationship we can replace <math>~K</math> with this expression to obtain,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~H(r)</math>
<math>~4\pi \biggl( \frac{G}{P_c}\biggr)^n M^{(n-1)} R_\mathrm{eq}^{(3-n)}
\biggl[ \frac{3M_\mathrm{tot}}{4\pi R_\mathrm{eq}^3} \biggr]^{(n+1)}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,028: Line 1,002:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~(n+1) \frac{P(r)}{\rho(r)} \, .</math>
<math>
~3 \biggl( \frac{5\mathfrak{f}_A \mathfrak{f}_M^2}{\mathfrak{f}_W} \biggr)^n
</math>
   </td>
   </td>
</tr>
</tr>
</table>
 
</div>
Hence,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~-\Phi(r)</math>
<math>\Rightarrow ~~~~ \biggl( \frac{G M_\mathrm{tot}^2}{P_c R_\mathrm{eq}^4}\biggr)^n
\biggl( \frac{3}{4\pi } \biggr)^{n}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,044: Line 1,017:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~(n+1) \frac{P(r)}{\rho(r)} + \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \, ,</math>
<math>
~\biggl( \frac{5\mathfrak{f}_A \mathfrak{f}_M^2}{\mathfrak{f}_W} \biggr)^n  
</math>
  </td>
</tr>
 
<tr>
  <td align="right" colspan="3">
<math>
\Rightarrow ~~~~ P_c = \frac{3 }{20\pi }\biggl( \frac{G M_\mathrm{tot}^2}{R_\mathrm{eq}^4} \biggr)
\cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \mathfrak{f}_M^2} \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
and,
Now, from our above [[User:Tohline/SSC/Virial/Polytropes#Gravitational_Potential_Energy|examination of the expression for the gravitational potential energy]], we know that,
<div align="center">
<div align="center">
<table border="0" cellpadding="5">
<table border="0" cellpadding="5" align="center">
 
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~W_\mathrm{grav}</math>
<math>~\frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,061: Line 1,044:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ - \frac{1}{2} \int_0^R \biggl[ (n+1) \frac{P(r)}{\rho(r)} + \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \biggr] 4\pi \rho(r) r^2 dr </math>
<math>~\frac{5}{5-n} \, .</math>
  </td>
</tr>
</table>
</div>
Hence, our expression for the central pressure becomes,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right" colspan="3">
<math>
~P_c = \frac{3 }{4\pi (5-n)}\biggl( \frac{G M_\mathrm{tot}^2}{R_\mathrm{eq}^4} \biggr)
\cdot \frac{1}{\mathfrak{f}_A }  \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
As it should, this precisely matches [[User:Tohline/SSC/Virial/Polytropes#Central_Pressure|the expression that we derived, above]], starting from [[User:Tohline/Appendix/References|Chandrasekhar's [C67]]] presentation.
====Gravitational Potential Energy====


END OF DELETION  -->
As has been [[User:Tohline/SphericallySymmetricConfigurations/Virial#AlternateGravPotEnergy|discussed elsewhere]], we have learned from [[User:Tohline/Appendix/References|Chandrasekhar's discussion of polytropic spheres [C67]]] &#8212; see his Equation (16), p. 64 &#8212; that if a spherically symmetric system is in hydrostatic balance, the total gravitational potential energy can be obtained from the following integral:
<div align="center">
<table border="0" cellpadding="5">
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~W_\mathrm{grav}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,073: Line 1,080:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ - 2\pi \biggl\{
<math>~ + \frac{1}{2} \int_0^R \Phi(r) dm \, .</math>
(n+1) \int_0^R P(r) r^2 dr
+ \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \int_0^R \rho(r) r^2 dr
\biggr\} </math>
   </td>
   </td>
</tr>
</tr>
 
</table>
</div>
Using "[[User:Tohline/SphericallySymmetricConfigurations/SolutionStrategies#Technique_3|technique #3]]" to solve the differential equation that governs the statement of hydrostatic balance, we know that in any polytropic sphere, <math>~\Phi(r)</math> is related to the configuration's radial enthalpy profile, <math>~H(r)</math>, via the algebraic expression,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\Phi(r) + H(r)</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,088: Line 1,096:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ - 2\pi \biggl\{
<math>~C_B \, ,</math>
\frac{1}{3} (n+1)P_c R_\mathrm{eq}^3 \int_0^1 3\biggl[ \frac{P(x)}{P_c} \biggr] x^2 dx
+ \frac{GM_\mathrm{tot}}{3R_\mathrm{eq}}  \biggl( \rho_c R_\mathrm{eq}^3  \biggr) \int_0^1  3 \biggl[ \frac{\rho(x)}{\rho_c} \biggr] x^2 dx
\biggr\} </math>
   </td>
   </td>
</tr>
</tr>
 
</table>
</div>
where, <math>~C_B</math>, is an integration constant.  At the surface of the equilibrium configuration, <math>~H = 0</math> and <math>~\Phi = - GM_\mathrm{tot}/R_\mathrm{eq}</math>, so the integration constant is,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~C_B</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,103: Line 1,112:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ - 2\pi \biggl\{
<math>~- \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \, ,</math>
\frac{1}{3} (n+1)P_c R_\mathrm{eq}^3 \mathfrak{f}_A
+ \frac{GM_\mathrm{tot}}{3R_\mathrm{eq}}  \biggl( \rho_c R_\mathrm{eq}^3  \biggr) \mathfrak{f}_M
\biggr\} </math>
   </td>
   </td>
</tr>
</tr>
 
</table>
</div>
which implies,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\Phi(r) </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,118: Line 1,128:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ - \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}} \biggl\{
<math>~ - H(r) - \frac{GM_\mathrm{tot}}{R_\mathrm{eq}}  \, .</math>
\frac{2\pi}{3} (n+1) \biggl[ \frac{P_c R_\mathrm{eq}^4}{GM_\mathrm{tot}^2} \biggr] \mathfrak{f}_A
+  \frac{1}{2} \biggl[ \frac{4\pi \rho_c R_\mathrm{eq}^3}{3M_\mathrm{tot}}  \biggr] \mathfrak{f}_M
\biggr\} </math>
   </td>
   </td>
</tr>
</tr>
 
</table>
</div>
Now, from [[User:Tohline/SR#Barotropic_Structure|our general discussion of barotropic relations]], we can write,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~H(r)</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,133: Line 1,144:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ - \frac{1}{2} \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}} \biggl\{
<math>~(n+1) \frac{P(r)}{\rho(r)} \, .</math>
\frac{4\pi}{3} (n+1) \biggl[ \frac{P_c R_\mathrm{eq}^4}{GM_\mathrm{tot}^2} \biggr] \mathfrak{f}_A
+  1
\biggr\} \, .</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
We now recall two earlier expressions that show the role that our structural form factors play in the evaluation of <math>~W</math> and <math>~P_c</math>, namely,
Hence,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~W_\mathrm{grav}</math>
<math>~-\Phi(r)</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,152: Line 1,160:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ - \frac{3}{5} \biggl( \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}} \biggr) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>
<math>~(n+1) \frac{P(r)}{\rho(r)} + \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \, ,</math>
   </td>
   </td>
</tr>
</tr>
Line 1,159: Line 1,167:
and,
and,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5">
 
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~P_c</math>
<math>~W_\mathrm{grav}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,168: Line 1,177:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ \frac{3 }{20\pi }\biggl( \frac{G M_\mathrm{tot}^2}{R_\mathrm{eq}^4} \biggr)
<math>~ - \frac{1}{2} \int_0^R \biggl[ (n+1) \frac{P(r)}{\rho(r)} + \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \biggr] 4\pi \rho(r) r^2 dr </math>
\cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \mathfrak{f}_M^2} \, .</math>
   </td>
   </td>
</tr>
</tr>
</table>
 
</div>
Plugging these into our newly derived expression for the gravitational potential energy gives,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~- \frac{3}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,185: Line 1,189:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ - \frac{1}{2} \biggl\{  
<math>~ - 2\pi \biggl\{  
\frac{4\pi}{3} (n+1) \biggl[ \frac{3 }{20\pi }\cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \mathfrak{f}_M^2} \biggr] \mathfrak{f}_A
(n+1) \int_0^R P(r) r^2 dr
+  1 \biggr\} </math>
+ \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \int_0^R  \rho(r) r^2 dr
\biggr\} </math>
   </td>
   </td>
</tr>
</tr>
Line 1,193: Line 1,198:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\Rightarrow ~~~~ (2\cdot 3) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,199: Line 1,204:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~  
<math>~ - 2\pi \biggl\{
(n+1) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} +  5 </math>
\frac{1}{3} (n+1)P_c R_\mathrm{eq}^3 \int_0^1 3\biggl[ \frac{P(x)}{P_c} \biggr] x^2 dx
+ \frac{GM_\mathrm{tot}}{3R_\mathrm{eq}}  \biggl( \rho_c R_\mathrm{eq}^3  \biggr) \int_0^1  3 \biggl[ \frac{\rho(x)}{\rho_c} \biggr] x^2 dx
\biggr\} </math>
   </td>
   </td>
</tr>
</tr>
Line 1,206: Line 1,213:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\Rightarrow ~~~~ (5 - n) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,212: Line 1,219:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~  5 </math>
<math>~ - 2\pi \biggl\{
\frac{1}{3} (n+1)P_c R_\mathrm{eq}^3 \mathfrak{f}_A
+ \frac{GM_\mathrm{tot}}{3R_\mathrm{eq}} \biggl( \rho_c R_\mathrm{eq}^3  \biggr) \mathfrak{f}_M
\biggr\} </math>
   </td>
   </td>
</tr>
</tr>
Line 1,218: Line 1,228:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\Rightarrow ~~~~ \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,224: Line 1,234:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~  \frac{5}{5-n} \, . </math>
<math>~ - \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}} \biggl\{
\frac{2\pi}{3} (n+1) \biggl[ \frac{P_c R_\mathrm{eq}^4}{GM_\mathrm{tot}^2} \biggr] \mathfrak{f}_A
+ \frac{1}{2} \biggl[ \frac{4\pi \rho_c R_\mathrm{eq}^3}{3M_\mathrm{tot}} \biggr] \mathfrak{f}_M
\biggr\} </math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
As it should, this agrees with the expression for the ratio, <math>\mathfrak{f}_W/\mathfrak{f}_M^2</math>, that was [[User:Tohline/SSC/Virial/Polytropes#Gravitational_Potential_Energy|derived in our above discussion of the gravitational potential energy]].


===Summary===
<tr>
In summary, expressions for the three structural form factors associated with isolated, spherically symmetric polytropes are as follows:
   <td align="right">
 
&nbsp;
<div align="center">
   </td>
<table border="1" align="center" cellpadding="5">
   <td align="center">
<tr><th align="center" colspan="1">
Structural Form Factors for <font color="red">Isolated</font> Polytropes
</th></tr>
<tr><td align="center">
 
<table border="0" cellpadding="5" align="center">
<tr>
   <td align="right">
<math>~\mathfrak{f}_M</math>
   </td>
   <td align="center">
<math>~=</math>
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\xi_1} </math>
<math>~ - \frac{1}{2} \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}} \biggl\{
\frac{4\pi}{3} (n+1) \biggl[ \frac{P_c R_\mathrm{eq}^4}{GM_\mathrm{tot}^2} \biggr] \mathfrak{f}_A
+  1
\biggr\} \, .</math>
   </td>
   </td>
</tr>
</tr>
 
</table>
</div>
We now recall two earlier expressions that show the role that our structural form factors play in the evaluation of <math>~W</math> and <math>~P_c</math>, namely,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\mathfrak{f}_W </math>
<math>~W_\mathrm{grav}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,262: Line 1,268:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{3^2\cdot 5}{5-n} \biggl[ \frac{\Theta^'}{\xi} \biggr]^2_{\xi_1} </math>
<math>~ - \frac{3}{5} \biggl( \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}} \biggr) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>
   </td>
   </td>
</tr>
</tr>
 
</table>
</div>
and,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\mathfrak{f}_A  </math>
<math>~P_c</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,274: Line 1,284:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~ \frac{3 }{20\pi }\biggl( \frac{G M_\mathrm{tot}^2}{R_\mathrm{eq}^4} \biggr)
\frac{3(n+1) }{(5-n)} ~\biggl[ \Theta^' \biggr]^2_{\xi_1}
\cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \mathfrak{f}_M^2} \, .</math>
</math>
   </td>
   </td>
</tr>
</table>
</td>
</tr>
</tr>
</table>
</table>
</div>
</div>
 
Plugging these into our newly derived expression for the gravitational potential energy gives,
==Nonrotating Adiabatic Configuration Embedded in an External Medium==
For a nonrotating configuration <math>~(C=J=0)</math> that is embedded in, and is influenced by the pressure <math>~P_e</math> of, an external medium, the statement of virial equilibrium is,
<div align="center">
<math>
3 B\chi_\mathrm{eq}^{3 -3\gamma_g} -~3A\chi_\mathrm{eq}^{-1}  -~ 3D\chi_\mathrm{eq}^3 = 0 \, .
</math>
</div>
 
 
====Solution Expressed in Terms of K and M (Whitworth's 1981 Relation)====
This is precisely the same condition that derives from setting equation (3) to zero in [http://adsabs.harvard.edu/abs/1981MNRAS.195..967W Whitworth's] (1981, MNRAS, 195, 967) discussion of the ''Global Gravitational Stability for One-dimensional Polytropes''.  The overlap with Whitworth's narative is clearer after introducing the algebraic expressions for the coefficients <math>~A</math>, <math>~B</math>, and <math>~D</math>, to obtain,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~4\pi \biggl( \frac{P_e}{P_\mathrm{norm}} \biggr) \chi_\mathrm{eq}^3 </math>
<math>~- \frac{3}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,307: Line 1,301:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~3 \biggl( \frac{4\pi}{3} \biggr)^{1-\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
<math>~ - \frac{1}{2} \biggl\{
\frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}} \cdot \chi_\mathrm{eq}^{3 -3\gamma_g}
\frac{4\pi}{3} (n+1) \biggl[ \frac{3 }{20\pi }\cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \mathfrak{f}_M^2} \biggr] \mathfrak{f}_A
~-~\frac{3}{5} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2 \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \cdot \chi_\mathrm{eq}^{-1} \, ;</math>
+  1 \biggr\} </math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
dividing the equation through by <math>~(4\pi \chi_\mathrm{eq}^3/P_\mathrm{norm})</math>,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~P_e </math>
<math>\Rightarrow ~~~~ (2\cdot 3) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,326: Line 1,315:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~P_\mathrm{norm} \biggl[ \biggl( \frac{3}{4\pi} \biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}}
<math>~  
\cdot \chi_\mathrm{eq}^{-3\gamma_g} ~- \biggl(\frac{3}{20\pi} \biggr) \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2
(n+1) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} +  5 </math>
\frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \cdot \chi_\mathrm{eq}^{-4} \biggr] </math>
   </td>
   </td>
</tr>
</tr>
Line 1,334: Line 1,322:
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>\Rightarrow ~~~~ (5 - n) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,340: Line 1,328:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~P_\mathrm{norm} R_\mathrm{norm}^4\biggl[ \biggl( \frac{3}{4\pi R_\mathrm{eq}^3} \biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
<math>~ 5 </math>
\frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}} \cdot R_\mathrm{norm}^{3\gamma_g-4}
- \biggl(\frac{3}{20\pi R_\mathrm{eq}^4} \biggr)\biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2 \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \biggr] \, ;</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
and inserting expressions for the [[User:Tohline/SphericallySymmetricConfigurations/Virial#Normalizations|parameter normalizations]] as defined in our accompanying [[User:Tohline/SphericallySymmetricConfigurations/Virial#Virial_Equilibrium_of_Spherically_Symmetric_Configurations|introductory discussion]] to obtain,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~P_e </math>
<math>\Rightarrow ~~~~ \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,359: Line 1,340:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~GM_\mathrm{tot}^2\biggl[ \biggl( \frac{3}{4\pi R_\mathrm{eq}^3} \biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
<math>~ \frac{5}{5-n} \, . </math>
\frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}} \cdot \frac{K M_\mathrm{tot}^{\gamma_g-2}}{G}
- \biggl(\frac{3}{20\pi R_\mathrm{eq}^4} \biggr) \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2 \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \biggr] </math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
As it should, this agrees with the expression for the ratio, <math>\mathfrak{f}_W/\mathfrak{f}_M^2</math>, that was [[User:Tohline/SSC/Virial/Polytropes#Gravitational_Potential_Energy|derived in our above discussion of the gravitational potential energy]].
===Summary===
In summary, expressions for the three structural form factors associated with isolated, spherically symmetric polytropes are as follows:


<div align="center">
<table border="1" align="center" cellpadding="5">
<tr><th align="center" colspan="1">
Structural Form Factors for <font color="red">Isolated</font> Polytropes
</th></tr>
<tr><td align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\mathfrak{f}_M</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,373: Line 1,366:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~K \biggl( \frac{3M_\mathrm{limit}}{4\pi R_\mathrm{eq}^3} \biggr)^{\gamma_g} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}}
<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\xi_1} </math>
- \biggl(\frac{3GM_\mathrm{limit}^2}{20\pi R_\mathrm{eq}^4} \biggr) \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \, .</math>
   </td>
   </td>
</tr>
</tr>
</table>
 
</div>
 
If the structural form factors are set equal to unity, this exactly matches equation (5) of [http://adsabs.harvard.edu/abs/1981MNRAS.195..967W Whitworth], which reads:
<div align="center">
<table border="2">
<tr><td>
[[File:Whitworth1981Eq5.jpg|500px|center|Whitworth (1981, MNRAS, 195, 967)]]
</td></tr>
</table>
</div>
 
Notice that, when <math>~P_e \rightarrow 0</math>, this expression reduces to the solution we obtained for an isolated polytrope, expressed in terms of <math>~K</math> and <math>~M_\mathrm{limit}</math> (see the left-hand column of our [[User:Tohline/SSC/Virial/Polytropes#TwoPointsOfView|table titled "Two Points of View"]]).
 
====Solution Expressed in Terms of M and Central Pressure====
Beginning again with the [[User:Tohline/SSC/Virial/Polytropes#Nonrotating_Adiabatic_Configuration_Embedded_in_an_External_Medium|relevant statement of virial equilibirum]], namely,
<div align="center">
<math>
A = B\chi_\mathrm{eq}^{4 -3\gamma_g}  -~ D\chi_\mathrm{eq}^4  \, ,
</math>
</div>
but adopting the alternate expression for the coefficient, <math>~B</math>, [[User:Tohline/SSC/Virial/Polytropes#Virial_Equilibrium|given above]], that is,
<div align="center">
<math>
B = \frac{4\pi}{3}
\biggl[ \biggl( \frac{P_c}{P_\mathrm{norm}} \biggr)\chi^{3\gamma} \biggr]_\mathrm{eq}
\cdot \mathfrak{f}_A \, ,
</math>
</div>
we can write,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\frac{1}{5} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W</math>
<math>\mathfrak{f}_W </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,418: Line 1,378:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>~\frac{3^2\cdot 5}{5-n} \biggl[ \frac{\Theta^'}{\xi} \biggr]^2_{\xi_1} </math>
\frac{4\pi}{3} \biggl[ \biggl( \frac{P_c}{P_\mathrm{norm}} \biggr)\chi^{3\gamma} \biggr]_\mathrm{eq} \mathfrak{f}_A
   </td>
\cdot \chi_\mathrm{eq}^{4 -3\gamma_g}
-~ \biggl( \frac{4\pi}{3} \biggr) \frac{P_e}{P_\mathrm{norm}} \chi_\mathrm{eq}^4
</math>
   </td>
</tr>
</tr>


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\Rightarrow~~~\frac{3}{20\pi} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W</math>
<math>\mathfrak{f}_A  </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,435: Line 1,390:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>
\biggl[ \biggl( \frac{P_c}{P_\mathrm{norm}} \biggr) \mathfrak{f}_A -~ \frac{P_e}{P_\mathrm{norm}} \biggr] \chi_\mathrm{eq}^4
\frac{3(n+1) }{(5-n)} ~\biggl[ \Theta^' \biggr]^2_{\xi_1}
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</td>
</tr>
</table>
</div>
==Nonrotating Adiabatic Configuration Embedded in an External Medium==
For a nonrotating configuration <math>~(C=J=0)</math> that is embedded in, and is influenced by the pressure <math>~P_e</math> of, an external medium, the statement of virial equilibrium is,
<div align="center">
<math>
3 B\chi_\mathrm{eq}^{3 -3\gamma_g} -~3A\chi_\mathrm{eq}^{-1}  -~ 3D\chi_\mathrm{eq}^3 = 0 \, .
</math>
</div>


====Solution Expressed in Terms of K and M (Whitworth's 1981 Relation)====
This is precisely the same condition that derives from setting equation (3) to zero in [http://adsabs.harvard.edu/abs/1981MNRAS.195..967W Whitworth's] (1981, MNRAS, 195, 967) discussion of the ''Global Gravitational Stability for One-dimensional Polytropes''.  The overlap with Whitworth's narative is clearer after introducing the algebraic expressions for the coefficients <math>~A</math>, <math>~B</math>, and <math>~D</math>, to obtain,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~4\pi \biggl( \frac{P_e}{P_\mathrm{norm}} \biggr) \chi_\mathrm{eq}^3 </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,449: Line 1,423:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>~3 \biggl( \frac{4\pi}{3} \biggr)^{1-\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
\biggl[ \mathfrak{f}_A P_c  -~ P_e\biggr] \frac{R_\mathrm{eq}^4}{G M_\mathrm{tot}^2}
\frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}} \cdot \chi_\mathrm{eq}^{3 -3\gamma_g}
</math>
~-~\frac{3}{5} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2 \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \cdot \chi_\mathrm{eq}^{-1} \, ;</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
dividing the equation through by <math>~(4\pi \chi_\mathrm{eq}^3/P_\mathrm{norm})</math>,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\Rightarrow ~~~ \frac{3}{20\pi} \biggl( \frac{G M_\mathrm{limit}^2}{R_\mathrm{eq}^4}\biggr)  \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} </math>
<math>~P_e </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,463: Line 1,442:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>~P_\mathrm{norm} \biggl[ \biggl( \frac{3}{4\pi} \biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}}
\mathfrak{f}_A P_c  -~ P_e \, .
\cdot \chi_\mathrm{eq}^{-3\gamma_g} ~- \biggl(\frac{3}{20\pi} \biggr) \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2
</math>
\frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \cdot \chi_\mathrm{eq}^{-4} \biggr] </math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
Again notice that, when <math>~P_e \rightarrow 0</math>, this expression reduces to the solution we obtained for an isolated polytrope, but this time expressed in terms of <math>~P_c</math> and <math>~M_\mathrm{limit}</math> (see the right-hand column of our [[User:Tohline/SSC/Virial/Polytropes#TwoPointsOfView|table titled "Two Points of View"]]).
====Contrast with Detailed Force-Balanced Solution====
As has just been demonstrated, the virial theorem provides a mathematical expression that allows us to ''relate'' the equilibrium radius of a configuration to the applied external pressure, once the configuration's mass and either its specific entropy or central pressure are specified.  In contrast to this, as has been [[User:Tohline/SSC/Structure/PolytropesEmbedded#Embedded_Polytropic_Spheres|discussed in detail in another chapter]], [http://adsabs.harvard.edu/abs/1970MNRAS.151...81H Horedt (1970)],  [http://adsabs.harvard.edu/abs/1981MNRAS.195..967W Whitworth (1981)] and [http://adsabs.harvard.edu/abs/1983ApJ...268..165S Stahler (1983)] have each derived separate analytic expressions for <math>~R_\mathrm{eq}</math> and <math>~P_e</math> &#8212; given in terms of the Lane-Emden function, <math>~\Theta</math>, and its radial derivative &#8212; without demonstrating how the equilibrium radius and external pressure directly relate to one another.  That is to say, solution of the detailed force-balanced equations provides a pair of equilibrium expressions that are parametrically related to one another through the Lane-Emden function.  For example &#8212; see our [[User:Tohline/SSC/Structure/PolytropesEmbedded#Horedt.27s_Presentation|related discussion for more details]] &#8212; Horedt derives the following set of parametric equations relating the configuration's dimensionless radius, <math>~r_a</math>, to a specified dimensionless bounding pressure, <math>~p_a</math>:
<div align="center">
<table border="0" cellpadding="3">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>
&nbsp;
~r_a \equiv \frac{R_\mathrm{eq}}{R_\mathrm{Horedt}}
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=~</math>
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~P_\mathrm{norm} R_\mathrm{norm}^4\biggl[ \biggl( \frac{3}{4\pi R_\mathrm{eq}^3} \biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
\tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)} \, ,
\frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}} \cdot R_\mathrm{norm}^{3\gamma_g-4}
</math>
- \biggl(\frac{3}{20\pi R_\mathrm{eq}^4} \biggr)\biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2 \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \biggr] \, ;</math>
   </td>
   </td>
</tr>
</tr>
 
</table>
</div>
and inserting expressions for the [[User:Tohline/SphericallySymmetricConfigurations/Virial#Normalizations|parameter normalizations]] as defined in our accompanying [[User:Tohline/SphericallySymmetricConfigurations/Virial#Virial_Equilibrium_of_Spherically_Symmetric_Configurations|introductory discussion]] to obtain,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>
<math>~P_e </math>
~p_a \equiv \frac{P_\mathrm{e}}{P_\mathrm{Horedt}}
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=~</math>
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~GM_\mathrm{tot}^2\biggl[ \biggl( \frac{3}{4\pi R_\mathrm{eq}^3} \biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
\tilde\theta_n^{n+1}( -\tilde\xi^2 \tilde\theta' )^{2(n+1)/(n-3)} \, ,
\frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}} \cdot \frac{K M_\mathrm{tot}^{\gamma_g-2}}{G}
</math>
- \biggl(\frac{3}{20\pi R_\mathrm{eq}^4} \biggr) \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2 \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \biggr] </math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
where,
<div align="center">
<table border="0" cellpadding="3">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>
&nbsp;
~R_\mathrm{Horedt}
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,525: Line 1,489:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~K \biggl( \frac{3M_\mathrm{limit}}{4\pi R_\mathrm{eq}^3} \biggr)^{\gamma_g} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}}
\biggl[ \frac{4\pi}{(n+1)^n}\biggl( \frac{G}{K} \biggr)^n M_\mathrm{limit}^{n-1} \biggr]^{1/(n-3)} \, ,
- \biggl(\frac{3GM_\mathrm{limit}^2}{20\pi R_\mathrm{eq}^4} \biggr) \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \, .</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>


<tr>
If the structural form factors are set equal to unity, this exactly matches equation (5) of [http://adsabs.harvard.edu/abs/1981MNRAS.195..967W Whitworth], which reads:
  <td align="right">
<div align="center">
<math>
<table border="2">
~P_\mathrm{Horedt}
<tr><td>
</math>
[[File:Whitworth1981Eq5.jpg|500px|center|Whitworth (1981, MNRAS, 195, 967)]]
  </td>
</td></tr>
  <td align="center">
</table>
<math>~=</math>
</div>
  </td>
 
  <td align="left">
Notice that, when <math>~P_e \rightarrow 0</math>, this expression reduces to the solution we obtained for an isolated polytrope, expressed in terms of <math>~K</math> and <math>~M_\mathrm{limit}</math> (see the left-hand column of our [[User:Tohline/SSC/Virial/Polytropes#TwoPointsOfView|table titled "Two Points of View"]]).
 
====Solution Expressed in Terms of M and Central Pressure====
Beginning again with the [[User:Tohline/SSC/Virial/Polytropes#Nonrotating_Adiabatic_Configuration_Embedded_in_an_External_Medium|relevant statement of virial equilibirum]], namely,
<div align="center">
<math>
A = B\chi_\mathrm{eq}^{4 -3\gamma_g}  -~ D\chi_\mathrm{eq}^4  \, ,
</math>
</div>
but adopting the alternate expression for the coefficient, <math>~B</math>, [[User:Tohline/SSC/Virial/Polytropes#Virial_Equilibrium|given above]], that is,
<div align="center">
<math>
<math>
K^{4n/(n-3)}\biggl[ \frac{(n+1)^3}{4\pi G^3 M_\mathrm{limit}^2} \biggr]^{(n+1)/(n-3)} \, .
B = \frac{4\pi}{3}  
\biggl[ \biggl( \frac{P_c}{P_\mathrm{norm}} \biggr)\chi^{3\gamma} \biggr]_\mathrm{eq}
\cdot \mathfrak{f}_A \, ,
</math>
</math>
  </td>
</tr>
</table>
</div>
</div>
 
we can write,
It is important to appreciate that, in the expressions for <math>~r_a</math> and <math>~p_a</math>, the tilde indicates that the Lane-Emden function and its derivative are to be evaluated, not at the radial coordinate, <math>~\xi_1</math>, that is traditionally associated with the "first zero" of the Lane-Emden function and therefore with the surface of the ''isolated polytrope,'' but at the radial coordinate, <math>~\tilde\xi</math>, where the internal pressure of the isolated polytrope equals <math>~P_e</math> and at which the ''embedded'' polytrope is to be truncated.  The coordinate, <math>~\tilde\xi</math>, therefore identifies the surface of the embedded &#8212; or, pressure-truncated &#8212; polytrope.  We also have taken the liberty of attaching the subscript "limit" to <math>~M</math> in both defining relations because it is clear that Hoerdt intended for the normalization mass to be the mass of the pressure-truncated object, not the mass of the associated ''isolated'' (and untruncated) polytrope.  In anticipation of further derivations, below, we note here the ratio of Hoerdt's normalization parameters to ours, assuming <math>~\gamma = (n+1)/n</math>:
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
Line 1,555: Line 1,528:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\biggl( \frac{R_\mathrm{Hoerdt}}{R_\mathrm{norm}} \biggr)^{n-3}</math>
<math>~\frac{1}{5} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,561: Line 1,534:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~  
<math>~
\biggl[ \frac{4\pi}{(n+1)^n}\biggl( \frac{G}{K} \biggr)^n M_\mathrm{limit}^{n-1} \biggr]
\frac{4\pi}{3} \biggl[ \biggl( \frac{P_c}{P_\mathrm{norm}} \biggr)\chi^{3\gamma} \biggr]_\mathrm{eq} \mathfrak{f}_A
\biggl[ \biggl( \frac{K}{G}\biggr)^n M_\mathrm{tot}^{1-n}\biggr]
\cdot \chi_\mathrm{eq}^{4 -3\gamma_g}
-~ \biggl( \frac{4\pi}{3} \biggr) \frac{P_e}{P_\mathrm{norm}} \chi_\mathrm{eq}^4
</math>
</math>
   </td>
   </td>
</tr>
</tr>


<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\Rightarrow~~~\frac{3}{20\pi} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,576: Line 1,551:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~  
<math>~
\frac{4\pi}{(n+1)^n} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)^{n-1} \, ,
\biggl[ \biggl( \frac{P_c}{P_\mathrm{norm}} \biggr) \mathfrak{f}_A -~ \frac{P_e}{P_\mathrm{norm}} \biggr] \chi_\mathrm{eq}^4
</math>
</math>
   </td>
   </td>
Line 1,584: Line 1,559:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\biggl( \frac{P_\mathrm{Hoerdt}}{P_\mathrm{norm}} \biggr)^{n-3}</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,590: Line 1,565:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~  
<math>~
K^{4n}\biggl[ \frac{(n+1)^3}{4\pi G^3 M_\mathrm{limit}^2} \biggr]^{n+1} \biggl[ \frac{G^{3(n+1)} M_\mathrm{tot}^{2(n+1)}}{K^{4n}} \biggr]
\biggl[ \mathfrak{f}_A P_c  -~ P_e\biggr] \frac{R_\mathrm{eq}^4}{G M_\mathrm{tot}^2}
</math>
</math>
   </td>
   </td>
Line 1,598: Line 1,573:
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>\Rightarrow ~~~ \frac{3}{20\pi} \biggl( \frac{G M_\mathrm{limit}^2}{R_\mathrm{eq}^4}\biggr)  \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,604: Line 1,579:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~  
<math>~
\biggl[ \frac{(n+1)^3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2}\biggr]^{n+1} \, .
\mathfrak{f}_A P_c  -~ P_e \, .
</math>
</math>
   </td>
   </td>
Line 1,612: Line 1,587:
</div>
</div>


Next, we demonstrate that this pair of parametric relations satisfies the virial theorem and, in so doing, demonstrate how <math>~r_a</math> and <math>~p_a</math> may be ''directly'' related to each other.  Given that Hoerdt's chosen normalization radius and normalization pressure are defined in terms of <math>~K</math> and <math>~M_\mathrm{limit}</math>, we begin with the [[User:Tohline/SSC/Virial/Polytropes#Solution_Expressed_in_Terms_of_K_and_M_.28Whitworth.27s_1981_Relation.2|virial theorem derived above]] in terms of <math>~K</math> and <math>~M_\mathrm{limit}</math>, setting <math>~\gamma_g = (n+1)/n</math>.
Again notice that, when <math>~P_e \rightarrow 0</math>, this expression reduces to the solution we obtained for an isolated polytrope, but this time expressed in terms of <math>~P_c</math> and <math>~M_\mathrm{limit}</math> (see the right-hand column of our [[User:Tohline/SSC/Virial/Polytropes#TwoPointsOfView|table titled "Two Points of View"]]).


====Contrast with Detailed Force-Balanced Solution====
As has just been demonstrated, the virial theorem provides a mathematical expression that allows us to ''relate'' the equilibrium radius of a configuration to the applied external pressure, once the configuration's mass and either its specific entropy or central pressure are specified.  In contrast to this, as has been [[User:Tohline/SSC/Structure/PolytropesEmbedded#Embedded_Polytropic_Spheres|discussed in detail in another chapter]], [http://adsabs.harvard.edu/abs/1970MNRAS.151...81H Horedt (1970)],  [http://adsabs.harvard.edu/abs/1981MNRAS.195..967W Whitworth (1981)] and [http://adsabs.harvard.edu/abs/1983ApJ...268..165S Stahler (1983)] have each derived separate analytic expressions for <math>~R_\mathrm{eq}</math> and <math>~P_e</math> &#8212; given in terms of the Lane-Emden function, <math>~\Theta</math>, and its radial derivative &#8212; without demonstrating how the equilibrium radius and external pressure directly relate to one another.  That is to say, solution of the detailed force-balanced equations provides a pair of equilibrium expressions that are parametrically related to one another through the Lane-Emden function.  For example &#8212; see our [[User:Tohline/SSC/Structure/PolytropesEmbedded#Horedt.27s_Presentation|related discussion for more details]] &#8212; Horedt derives the following set of parametric equations relating the configuration's dimensionless radius, <math>~r_a</math>, to a specified dimensionless bounding pressure, <math>~p_a</math>:
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="3">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~P_e </math>
<math>
~r_a \equiv \frac{R_\mathrm{eq}}{R_\mathrm{Horedt}}
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
<math>~=~</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~K \biggl( \frac{3M_\mathrm{limit}}{4\pi R_\mathrm{eq}^3} \biggr)^{(n+1)/n} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{(n+1)/n}}
<math>
- \biggl(\frac{3GM_\mathrm{limit}^2}{20\pi R_\mathrm{eq}^4} \biggr) \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \, .</math>
\tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)} \, ,
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
After setting <math>~R_\mathrm{eq} = r_a R_\mathrm{Horedt} </math>, a bit of algebraic manipulation shows that the first term on the right-hand side of the virial equilibrium expression becomes,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~
<math>
K \biggl( \frac{3M_\mathrm{limit}}{4\pi R_\mathrm{eq}^3} \biggr)^{(n+1)/n} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{(n+1)/n}}
~p_a \equiv \frac{P_\mathrm{e}}{P_\mathrm{Horedt}}
</math>
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
<math>~=~</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>
r_a^{-3(n+1)/n} \mathfrak{f}_A \biggl[ \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{n-3} \frac{(n+1)^{3n}}{(4\pi)^n}\biggr]^{(n+1)/[n(n-3)]}
\tilde\theta_n^{n+1}( -\tilde\xi^2 \tilde\theta' )^{2(n+1)/(n-3)} \, ,
[K^{4n} G^{-3(n+1)} M_\mathrm{limit}^{-2(n+1)} ]^{1/(n-3)} \, ,
</math>
</math>
   </td>
   </td>
Line 1,654: Line 1,627:
</table>
</table>
</div>
</div>
while the second term on the right-hand side becomes,
where,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="3">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~
<math>
\biggl(\frac{3GM_\mathrm{limit}^2}{20\pi R_\mathrm{eq}^4} \biggr) \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M}  
~R_\mathrm{Horedt}
</math>
</math>
   </td>
   </td>
Line 1,668: Line 1,641:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>
\frac{3}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \cdot r_a^{-4} (4\pi)^{-(n+1)/(n-3)} (n+1)^{4n/(n-3)}~
\biggl[ \frac{4\pi}{(n+1)^n}\biggl( \frac{G}{K} \biggr)^n M_\mathrm{limit}^{n-1} \biggr]^{1/(n-3)} \, ,
[K^{4n} G^{-3(n+1)} M_\mathrm{limit}^{-2(n+1)} ]^{1/(n-3)} \, .
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
But, using Horedt's expression for <math>~P_e</math>, the left-hand side of the virial equilibrium equation becomes,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~P_e = p_a P_\mathrm{Hoerdt}</math>
<math>
~P_\mathrm{Horedt}
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,688: Line 1,657:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>
p_a~(4\pi)^{-(n+1)/(n-3)} ~(n+1)^{3(n+1)/(n-3)}
K^{4n/(n-3)}\biggl[ \frac{(n+1)^3}{4\pi G^3 M_\mathrm{limit}^2} \biggr]^{(n+1)/(n-3)} \, .
[K^{4n} G^{-3(n+1)} M_\mathrm{limit}^{-2(n+1)} ]^{1/(n-3)} \, .
</math>
</math>
   </td>
   </td>
Line 1,696: Line 1,664:
</table>
</table>
</div>
</div>
Hence, the statement of virial equilibrium is,
 
It is important to appreciate that, in the expressions for <math>~r_a</math> and <math>~p_a</math>, the tilde indicates that the Lane-Emden function and its derivative are to be evaluated, not at the radial coordinate, <math>~\xi_1</math>, that is traditionally associated with the "first zero" of the Lane-Emden function and therefore with the surface of the ''isolated polytrope,'' but at the radial coordinate, <math>~\tilde\xi</math>, where the internal pressure of the isolated polytrope equals <math>~P_e</math> and at which the ''embedded'' polytrope is to be truncated.  The coordinate, <math>~\tilde\xi</math>, therefore identifies the surface of the embedded &#8212; or, pressure-truncated &#8212; polytrope.  We also have taken the liberty of attaching the subscript "limit" to <math>~M</math> in both defining relations because it is clear that Hoerdt intended for the normalization mass to be the mass of the pressure-truncated object, not the mass of the associated ''isolated'' (and untruncated) polytrope.  In anticipation of further derivations, below, we note here the ratio of Hoerdt's normalization parameters to ours, assuming <math>~\gamma = (n+1)/n</math>:
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
Line 1,702: Line 1,671:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~
<math>~\biggl( \frac{R_\mathrm{Hoerdt}}{R_\mathrm{norm}} \biggr)^{n-3}</math>
p_a~
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,710: Line 1,677:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>~  
\biggr\{ r_a^{-3(n+1)/n} \mathfrak{f}_A \biggl[ \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{n-3} \frac{(n+1)^{3n}}{(4\pi)^n}\biggr]^{(n+1)/[n(n-3)]}
\biggl[ \frac{4\pi}{(n+1)^n}\biggl( \frac{G}{K} \biggr)^n M_\mathrm{limit}^{n-1} \biggr]
\biggl[ \biggl( \frac{K}{G}\biggr)^n M_\mathrm{tot}^{1-n}\biggr]
</math>
</math>
   </td>
   </td>
Line 1,721: Line 1,689:
   </td>
   </td>
   <td align="center">
   <td align="center">
&nbsp;
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~~
<math>~  
- \frac{3}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \cdot r_a^{-4} (4\pi)^{-(n+1)/(n-3)} (n+1)^{4n/(n-3)} \biggr\}(4\pi)^{(n+1)/(n-3)} ~(n+1)^{-3(n+1)/(n-3)}
\frac{4\pi}{(n+1)^n} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)^{n-1} \, ,
</math>
</math>
   </td>
   </td>
Line 1,732: Line 1,700:
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\biggl( \frac{P_\mathrm{Hoerdt}}{P_\mathrm{norm}} \biggr)^{n-3}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,738: Line 1,706:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>~  
\mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M \cdot r_a^3} \biggr)^{(n+1)/n}  
K^{4n}\biggl[ \frac{(n+1)^3}{4\pi G^3 M_\mathrm{limit}^2} \biggr]^{n+1} \biggl[ \frac{G^{3(n+1)} M_\mathrm{tot}^{2(n+1)}}{K^{4n}} \biggr]
- \frac{3(n+1)}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \cdot r_a^{-4} \, ;
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>


or, multiplying through by <math>~r_a^4</math> and rearranging terms,
<tr>
 
<div align="center">
<table border="1" align="center" cellpadding="8">
<tr><td align="center">
 
<table border="0" cellpadding="5" align="center">
<tr>
   <td align="right">
   <td align="right">
<math>~
&nbsp;
\mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} r_a^{(n-3)/n} - p_a r_a^4
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,764: Line 1,720:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>~  
\frac{3(n+1)}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \, .
\biggl[ \frac{(n+1)^3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2}\biggr]^{n+1} \, .
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</td></tr>
</table>
</table>
</div>
</div>


Now, Hoerdt has given analytic expressions for <math>~r_a</math> and <math>~p_a</math> in terms of the Lane-Emden function and its first derivative.  The question is, what should the expressions for our structural form factors be in order for this virial expression to hold true for all pressure-truncated polytropic structures?  As has been [[User:Tohline/SSC/Virial/Polytropes#Summary|summarized above]], in the case of an ''isolated'' polytrope, whose surface is located at <math>~\xi_1</math> and whose global properties are defined by evaluation of the Lane-Emden function at <math>~\xi_1</math>, we know that (see the [[User:Tohline/SSC/Virial/Polytropes#Summary|above summary]]),
Next, we demonstrate that this pair of parametric relations satisfies the virial theorem and, in so doing, demonstrate how <math>~r_a</math> and <math>~p_a</math> may be ''directly'' related to each other.  Given that Hoerdt's chosen normalization radius and normalization pressure are defined in terms of <math>~K</math> and <math>~M_\mathrm{limit}</math>, we begin with the [[User:Tohline/SSC/Virial/Polytropes#Solution_Expressed_in_Terms_of_K_and_M_.28Whitworth.27s_1981_Relation.2|virial theorem derived above]] in terms of <math>~K</math> and <math>~M_\mathrm{limit}</math>, setting <math>~\gamma_g = (n+1)/n</math>.


<div align="center">
<div align="center">
<table border="0" align="center" cellpadding="5">
<table border="0" cellpadding="5" align="center">
<tr><th align="center" colspan="1">
Structural Form Factors for <font color="red">Isolated</font> Polytropes
</th></tr>
<tr><td align="center">


<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\mathfrak{f}_M</math>
<math>~P_e </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,793: Line 1,741:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\xi_1} </math>
<math>~K \biggl( \frac{3M_\mathrm{limit}}{4\pi R_\mathrm{eq}^3} \biggr)^{(n+1)/n} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{(n+1)/n}}
- \biggl(\frac{3GM_\mathrm{limit}^2}{20\pi R_\mathrm{eq}^4} \biggr) \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \, .</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
After setting <math>~R_\mathrm{eq} = r_a R_\mathrm{Horedt} </math>, a bit of algebraic manipulation shows that the first term on the right-hand side of the virial equilibrium expression becomes,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\mathfrak{f}_W </math>
<math>~
K \biggl( \frac{3M_\mathrm{limit}}{4\pi R_\mathrm{eq}^3} \biggr)^{(n+1)/n} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{(n+1)/n}}
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,805: Line 1,762:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{3^2\cdot 5}{5-n} \biggl[ \frac{\Theta^'}{\xi} \biggr]^2_{\xi_1} </math>
<math>~
r_a^{-3(n+1)/n} \mathfrak{f}_A \biggl[ \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{n-3} \frac{(n+1)^{3n}}{(4\pi)^n}\biggr]^{(n+1)/[n(n-3)]}
[K^{4n} G^{-3(n+1)} M_\mathrm{limit}^{-2(n+1)} ]^{1/(n-3)} \, ,
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
while the second term on the right-hand side becomes,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\mathfrak{f}_A  </math>
<math>~
\biggl(\frac{3GM_\mathrm{limit}^2}{20\pi R_\mathrm{eq}^4} \biggr) \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M}
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,817: Line 1,784:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~
\frac{3(n+1) }{(5-n)} ~\biggl[ \Theta^' \biggr]^2_{\xi_1} 
\frac{3}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \cdot r_a^{-4} (4\pi)^{-(n+1)/(n-3)} (n+1)^{4n/(n-3)}~
[K^{4n} G^{-3(n+1)} M_\mathrm{limit}^{-2(n+1)} ]^{1/(n-3)} \, .
</math>
</math>
   </td>
   </td>
</tr>
</table>
</td>
</tr>
</tr>
</table>
</table>
</div>
</div>
These same expressions may or may not work for pressure-truncated polytropes, even if the evaluation radius is shifted from <math>~\xi_1</math> to <math>~\tilde\xi</math>.  Let's see &hellip;
But, using Horedt's expression for <math>~P_e</math>, the left-hand side of the virial equilibrium equation becomes,
 
Inserting Hoerdt's expressions for <math>~r_a</math> and <math>~p_a</math> into the viral equilibrium expression, we have,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
Line 1,836: Line 1,798:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~
<math>~P_e = p_a P_\mathrm{Hoerdt}</math>
\frac{3(n+1)}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,845: Line 1,805:
   <td align="left">
   <td align="left">
<math>~
<math>~
\mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} [ \tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)} ]^{(n-3)/n}
p_a~(4\pi)^{-(n+1)/(n-3)} ~(n+1)^{3(n+1)/(n-3)}
~-~
[K^{4n} G^{-3(n+1)} M_\mathrm{limit}^{-2(n+1)} ]^{1/(n-3)} \, .
\tilde\theta_n^{n+1}( -\tilde\xi^2 \tilde\theta' )^{2(n+1)/(n-3)} [ \tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)} ]^{4}
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
Hence, the statement of virial equilibrium is,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~
p_a~
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,861: Line 1,827:
   <td align="left">
   <td align="left">
<math>~
<math>~
\mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} [ \tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)} ]^{(n-3)/n}
\biggr\{ r_a^{-3(n+1)/n} \mathfrak{f}_A \biggl[ \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{n-3} \frac{(n+1)^{3n}}{(4\pi)^n}\biggr]^{(n+1)/[n(n-3)]}
~-~
\tilde\theta_n^{n+1} \tilde\xi^4 [( -\tilde\xi^2 \tilde\theta' )^{2(n+1)+4(1-n)}  ]^{1/(n-3)}  
</math>
</math>
   </td>
   </td>
Line 1,873: Line 1,837:
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
&nbsp;
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>~~
\mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} [ \tilde\xi^{(n-3)} ( -\tilde\xi^2 \tilde\theta' )^{(1-n)}  ]^{1/n}
- \frac{3}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \cdot r_a^{-4} (4\pi)^{-(n+1)/(n-3)} (n+1)^{4n/(n-3)} \biggr\}(4\pi)^{(n+1)/(n-3)} ~(n+1)^{-3(n+1)/(n-3)}
~-~
\tilde\theta_n^{n+1} \tilde\xi^4 [( -\tilde\xi^2 \tilde\theta' )^{-2} ]
</math>
</math>
   </td>
   </td>
Line 1,893: Line 1,855:
   <td align="left">
   <td align="left">
<math>~
<math>~
\mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} \tilde\xi^{-(n+1)/n} ( -\tilde\theta' )^{(1-n)/n}
\mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M \cdot r_a^3} \biggr)^{(n+1)/n}  
~-~
- \frac{3(n+1)}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \cdot r_a^{-4} \, ;
\frac{\tilde\theta_n^{n+1} }{( -\tilde\theta' )^{2} } \, .
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
Assuming that the structural form factor, <math>~\mathfrak{f}_M</math>, has the same functional expression as in the case of isolated polytropes (but evaluated at <math>~\tilde\xi</math> instead of at <math>~\xi_1</math>), the virial relation further reduces to the form,
 
or, multiplying through by <math>~r_a^4</math> and rearranging terms,
 
<div align="center">
<div align="center">
<table border="1" align="center" cellpadding="8">
<tr><td align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~
<math>~
\frac{\tilde\theta_n^{n+1} }{( -\tilde\theta' )^{2} }
\mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} r_a^{(n-3)/n} - p_a r_a^4
</math>
</math>
   </td>
   </td>
Line 1,917: Line 1,881:
   <td align="left">
   <td align="left">
<math>~
<math>~
\mathfrak{f}_A \biggl( \frac{\tilde\xi}{- \tilde\theta'} \biggr)^{(n+1)/n} \tilde\xi^{-(n+1)/n} ( -\tilde\theta' )^{(1-n)/n}
\frac{3(n+1)}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \, .
- \biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \frac{\tilde\xi^2}{(-\tilde\theta^')^2} \cdot \mathfrak{f}_W
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>


</td></tr>
</table>
</div>
Now, Hoerdt has given analytic expressions for <math>~r_a</math> and <math>~p_a</math> in terms of the Lane-Emden function and its first derivative.  The question is, what should the expressions for our structural form factors be in order for this virial expression to hold true for all pressure-truncated polytropic structures?  As has been [[User:Tohline/SSC/Virial/Polytropes#Summary|summarized above]], in the case of an ''isolated'' polytrope, whose surface is located at <math>~\xi_1</math> and whose global properties are defined by evaluation of the Lane-Emden function at <math>~\xi_1</math>, we know that (see the [[User:Tohline/SSC/Virial/Polytropes#Summary|above summary]]),
<div align="center">
<table border="0" align="center" cellpadding="5">
<tr><th align="center" colspan="1">
Structural Form Factors for <font color="red">Isolated</font> Polytropes
</th></tr>
<tr><td align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\mathfrak{f}_M</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,931: Line 1,909:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\xi_1} </math>
\frac{\mathfrak{f}_A}{(- \tilde\theta' )^2} - \biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \frac{\tilde\xi^2}{(-\tilde\theta^')^2} \cdot \mathfrak{f}_W
</math>
   </td>
   </td>
</tr>
</tr>
Line 1,939: Line 1,915:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~
<math>\mathfrak{f}_W </math>
\Rightarrow~~~\tilde\theta^{n+1}  
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,947: Line 1,921:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>~\frac{3^2\cdot 5}{5-n} \biggl[ \frac{\Theta^'}{\xi} \biggr]^2_{\xi_1} </math>
\mathfrak{f}_A -  
\biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \tilde\xi^2 \cdot \mathfrak{f}_W 
</math>
   </td>
   </td>
</tr>
</tr>
Line 1,956: Line 1,927:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~
<math>\mathfrak{f}_A </math>
\Rightarrow~~~\frac{\mathfrak{f}_A - \tilde\theta^{n+1} }{\mathfrak{f}_W}
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,964: Line 1,933:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>
\biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \tilde\xi^2 \, .
\frac{3(n+1) }{(5-n)} ~\biggl[ \Theta^' \biggr]^2_{\xi_1}  
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>


</td>
</tr>
</table>
</table>
</div>
</div>
While this does not give us individual expressions for the form factors, <math>~\mathfrak{f}_W</math> and <math>~\mathfrak{f}_W</math>, the expression derived for the ratio of the form factors makes sense because the term that has been subtracted from <math>~\mathfrak{f}_A</math> in the numerator on the lefthand side, that is, <math>\tilde\theta^{n+1}</math>, naturally goes to zero in the limit of <math>~\tilde\xi \rightarrow \xi_1</math>, producing the correct expression for the ratio, <math>\mathfrak{f}_A/\mathfrak{f}_W</math>, in ''isolated polytropes''In summary, then, we have,
These same expressions may or may not work for pressure-truncated polytropes, even if the evaluation radius is shifted from <math>~\xi_1</math> to <math>~\tilde\xi</math>.  Let's see &hellip;


<div align="center" id="PTtable">
Inserting Hoerdt's expressions for <math>~r_a</math> and <math>~p_a</math> into the viral equilibrium expression, we have,
<table border="1" align="center" cellpadding="5">
<div align="center">
<tr><th align="center" colspan="1">
<table border="0" cellpadding="5" align="center">
Structural Form Factors for <font color="red">Pressure-Truncated</font> Polytropes
</th></tr>
<tr><td align="center">


<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\tilde\mathfrak{f}_M</math>
<math>~
\frac{3(n+1)}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 1,990: Line 1,960:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\tilde\xi} </math>
<math>~
\mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} [ \tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)} ]^{(n-3)/n}
~-~
\tilde\theta_n^{n+1}( -\tilde\xi^2 \tilde\theta' )^{2(n+1)/(n-3)} [ \tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)}  ]^{4}
</math>
   </td>
   </td>
</tr>
</tr>
Line 1,996: Line 1,970:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~
&nbsp;
~\frac{\tilde\mathfrak{f}_A - \tilde\theta^{n+1} }{\tilde\mathfrak{f}_W}
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,005: Line 1,977:
   <td align="left">
   <td align="left">
<math>~
<math>~
\biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \tilde\xi^2  
\mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} [ \tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)}  ]^{(n-3)/n}
~-~
\tilde\theta_n^{n+1} \tilde\xi^4 [( -\tilde\xi^2 \tilde\theta' )^{2(n+1)+4(1-n)}  ]^{1/(n-3)}
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>


</td>
</tr>
</table>
</div>
Notice that, in an effort to differentiate them from their counterparts developed earlier for "isolated" polytropes, we have affixed a tilde to each of these three form-factors, <math>~\mathfrak{f}_i</math>.
{{LSU_WorkInProgress}}
====Example====
=====Outline=====
Let's identify an equilibrium configuration numerically, using the free-energy expression.  From [[User:Tohline/SphericallySymmetricConfigurations/Virial#Gathering_it_all_Together|our introductory discussion]], the relevant expression is,
<div align="center">
<math>
\mathfrak{G}^* =
-3\mathcal{A} \chi^{-1} -~ \frac{1}{(1-\gamma_g)} \mathcal{B} \chi^{3-3\gamma_g} +~ \mathcal{D}\chi^3 \, ,
</math>
</div>
where,
<div align="center">
<table border="0" cellpadding="5">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\mathcal{A}</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~\equiv</math>
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>\frac{1}{5} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W \, ,</math>
<math>~
\mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} [ \tilde\xi^{(n-3)} ( -\tilde\xi^2 \tilde\theta' )^{(1-n)} ]^{1/n}
~-~
\tilde\theta_n^{n+1} \tilde\xi^4 [( -\tilde\xi^2 \tilde\theta' )^{-2} ]
</math>
   </td>
   </td>
</tr>
</tr>
Line 2,047: Line 2,002:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\mathcal{B}</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~\equiv</math>
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~
\frac{4\pi}{3}
\mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n}  \tilde\xi^{-(n+1)/n} ( -\tilde\theta' )^{(1-n)/n}   
\biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr) \frac{1}{\mathfrak{f}_M} \biggr]_\mathrm{eq}^{\gamma}
~-~
\cdot \mathfrak{f}_A
\frac{\tilde\theta_n^{n+1} }{( -\tilde\theta' )^{2} } \, .
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
Assuming that the structural form factor, <math>~\mathfrak{f}_M</math>, has the same functional expression as in the case of isolated polytropes (but evaluated at <math>~\tilde\xi</math> instead of at <math>~\xi_1</math>), the virial relation further reduces to the form,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~
\frac{\tilde\theta_n^{n+1} }{( -\tilde\theta' )^{2} }
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,069: Line 2,032:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~
\frac{4\pi}{3}
\mathfrak{f}_A \biggl( \frac{\tilde\xi}{- \tilde\theta'} \biggr)^{(n+1)/n} \tilde\xi^{-(n+1)/n} ( -\tilde\theta' )^{(1-n)/n}
\biggl[ \biggl( \frac{P_c}{P_\mathrm{norm}} \biggr)\chi^{3\gamma} \biggr]_\mathrm{eq}  
- \biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \frac{\tilde\xi^2}{(-\tilde\theta^')^2} \cdot \mathfrak{f}_W
\cdot \mathfrak{f}_A \, ,
</math>
</math>
   </td>
   </td>
Line 2,079: Line 2,041:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\mathcal{D}</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~\equiv</math>
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~
\biggl( \frac{4\pi}{3} \biggr) \frac{P_e}{P_\mathrm{norm}} \, .
\frac{\mathfrak{f}_A}{(- \tilde\theta' )^2} - \biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \frac{\tilde\xi^2}{(-\tilde\theta^')^2} \cdot \mathfrak{f}_W
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
<div align="center">
<table border="1" cellpadding="10" align="center">
<tr><td align="left">
For later use, note that,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\biggl( \frac{\mathcal{A}}{\mathcal{B}} \biggr)^n</math>
<math>~
\Rightarrow~~~\tilde\theta^{n+1}  
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,109: Line 2,063:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\biggl\{ 
<math>~
\frac{3}{20\pi} \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W
\mathfrak{f}_A -
\biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr\frac{1}{\mathfrak{f}_M} \biggr]^{-(n+1)/n}
\biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \tilde\xi^2 \cdot \mathfrak{f}_W 
\cdot \mathfrak{f}_A^{-1}
</math>
\biggr\}^n</math>
   </td>
   </td>
</tr>
</tr>
Line 2,119: Line 2,072:
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~
\Rightarrow~~~\frac{\mathfrak{f}_A - \tilde\theta^{n+1} }{\mathfrak{f}_W}
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,125: Line 2,080:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~5^{-n}
<math>~
\biggl( \frac{3}{4\pi} \biggr)^n \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^{2n}
\biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \tilde\xi^2 \, .
\biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr) \frac{1}{\mathfrak{f}_M} \biggr]^{-(n+1)}
\cdot \biggl( \frac{\mathfrak{f}_W}{\mathfrak{f}_A} \biggr)^{n}
</math>
</math>
   </td>
   </td>
</tr>
</tr>


</table>
</div>
While this does not give us individual expressions for the form factors, <math>~\mathfrak{f}_W</math> and <math>~\mathfrak{f}_W</math>, the expression derived for the ratio of the form factors makes sense because the term that has been subtracted from <math>~\mathfrak{f}_A</math> in the numerator on the lefthand side, that is, <math>\tilde\theta^{n+1}</math>, naturally goes to zero in the limit of <math>~\tilde\xi \rightarrow \xi_1</math>, producing the correct expression for the ratio, <math>\mathfrak{f}_A/\mathfrak{f}_W</math>, in ''isolated polytropes''.  In summary, then, we have,
<div align="center" id="PTtable">
<table border="1" align="center" cellpadding="5">
<tr><th align="center" colspan="1">
Structural Form Factors for <font color="red">Pressure-Truncated</font> Polytropes
</th></tr>
<tr><td align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\tilde\mathfrak{f}_M</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,141: Line 2,106:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{1}{5^n} \biggl( \frac{4\pi}{3} \biggr)  \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)^{n-1}
<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\tilde\xi} </math>
\cdot \frac{\mathfrak{f}_W^n}{\mathfrak{f}_A^n \mathfrak{f}_M^{1-n}} \, ;
</math>
   </td>
   </td>
</tr>
</tr>
</table>
 
</div>
and,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\frac{\mathcal{B}^{4n}}{\mathcal{A}^{3(n+1)}}</math>
<math>~
~\frac{\tilde\mathfrak{f}_A - \tilde\theta^{n+1} }{\tilde\mathfrak{f}_W}
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,160: Line 2,120:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\biggl\{
<math>~
\frac{1}{5} \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W \biggr\}^{-3(n+1)}
\biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \tilde\xi^2
\biggl\{ \frac{4\pi}{3}
</math>
\biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr\frac{1}{\mathfrak{f}_M} \biggr]^{(n+1)/n}
\cdot \mathfrak{f}_A
\biggr\}^{4n}</math>
   </td>
   </td>
</tr>
</tr>
</table>


<tr>
</td>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
5^{3(n+1)}  \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^{-6(n+1)}
\biggl( \frac{4\pi}{3} \biggr)^{4n-4(n+1)}
\biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)  \frac{1}{\mathfrak{f}_M} \biggr]^{4(n+1)} \cdot\frac{\mathfrak{f}_A^{4n}}{\mathfrak{f}_W^{3(n+1)}}
</math>
  </td>
</tr>
</tr>
</table>
</div>


<tr>
Notice that, in an effort to differentiate them from their counterparts developed earlier for "isolated" polytropes, we have affixed a tilde to each of these three form-factors, <math>~\mathfrak{f}_i</math>.
 
====Renormalization====
 
=====Grunt Work=====
 
Returning to the dimensionless form of the virial expression and multiplying through by <math>~[-\chi_\mathrm{eq}/(3D)]</math>, we obtain,
<div align="center">
<math>
\chi_\mathrm{eq}^4 = \frac{B}{D} \chi_\mathrm{eq}^{4-3\gamma_g} - \frac{A}{D} \, ,
</math>
</div>
or, after plugging in [[User:Tohline/SphericallySymmetricConfigurations/Virial#Gathering_it_all_Together|definitions of the coefficients]], <math>~A</math>, <math>~B</math>, and <math>~D</math>, and rewriting <math>~\chi_\mathrm{eq}</math> explicitly as <math>~R_\mathrm{eq}/R_\mathrm{norm}</math>,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\biggl( \frac{R_\mathrm{eq}}{R_\mathrm{norm}} \biggr)^4  </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,193: Line 2,155:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>  
5^{3(n+1)} \biggl( \frac{3}{4\pi} \biggr)^{4} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2(n+1)}  
\biggl(\frac{3}{4\pi}\biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
\cdot\frac{\mathfrak{f}_A^{4n} \mathfrak{f}_M^{2(n+1)} }{\mathfrak{f}_W^{3(n+1)}}
\biggl( \frac{P_e}{P_\mathrm{norm}} \biggr)^{-1} \frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_M^{\gamma_g}}
</math>
\biggl( \frac{R_\mathrm{eq}}{R_\mathrm{norm}} \biggr)^{4-3\gamma_g} -
\frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2} \biggl( \frac{P_e}{P_\mathrm{norm}} \biggr)^{-1}  
\frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_M^2} \, .</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
 
This relation can be written in a more physically concise form, as follows.  First, normalize <math>~P_e</math> to a new pressure scale &#8212; call it <math>~P_\mathrm{ad}</math> &#8212; and multiply through by <math>~(R_\mathrm{norm}/R_\mathrm{ad})^4</math> in order to normalizing <math>~R_\mathrm{eq}</math> to a new length scale,<math>~R_\mathrm{ad}</math>:
</td></tr>
</table>
</div>
 
Now, we could just blindly start setting values of the three leading coefficients, <math>~\mathcal{A}</math>, <math>~\mathcal{B}</math>, and <math>~\mathcal{D}</math>, then plot <math>~\mathfrak{G}^*(\chi)</math> to look for extrema.  But let's accept a little guidance from this chapter's virial analysis before choosing the coefficient values.  For embedded polytropes, we know that the structural form factors are,
 
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\tilde\mathfrak{f}_M = \frac{\bar\rho}{\rho_c}</math>
<math>~\biggl( \frac{R_\mathrm{eq}}{R_\mathrm{ad}} \biggr)^4  </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,218: Line 2,177:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\tilde\xi} \, ,</math>
<math>  
   </td>
\biggl(\frac{3}{4\pi}\biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
\biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{P_e}{P_\mathrm{ad}} \biggr)^{-1} \frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_M^{\gamma_g}}
\biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{3\gamma_g}\biggl( \frac{R_\mathrm{eq}}{R_\mathrm{ad}} \biggr)^{4-3\gamma_g}
</math>
   </td>
</tr>
</tr>


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\tilde\mathfrak{f}_W </math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
&nbsp;
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{3^2\cdot 5}{5-n} \biggl[ \frac{\Theta^'}{\xi} \biggr]^2_{\tilde\xi} = \biggl( \frac{5}{5-n} \biggr) \tilde\mathfrak{f}_M^2 \, ,</math>
<math>  
~-
\frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2} \biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr)
\frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_M^2} \biggl( \frac{P_e}{P_\mathrm{ad}} \biggr)^{-1} \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{4} \, ,
</math>
   </td>
   </td>
</tr>
</tr>
 
</table>
</div>
or,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\tilde\mathfrak{f}_A = \frac{\bar{P}}{P_c}</math>
<math>~\Chi_\mathrm{ad}^4 </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,242: Line 2,213:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>  
\frac{3(n+1) }{(5-n)} ~\biggl( \Theta^' \biggr)^2_{\tilde\xi} + \tilde\Theta^{n+1} \, .
\biggl(\frac{3}{4\pi}\biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
</math>
\biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{3\gamma_g}
\frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_M^{\gamma_g}}\cdot \frac{\Chi_\mathrm{ad}^{4-3\gamma_g} }{\Pi_\mathrm{ad}} -
\frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2}
\biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{4}
\frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_M^2} \cdot \frac{1}{\Pi_\mathrm{ad}}  \, ,</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
Hence, the coefficient expressions become,
where,
<div align="center">
<div align="center">
<table border="0" cellpadding="5">
<table border="0" cellpadding="5" align="center">
 
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\mathcal{A}</math>
<math>~\Chi_\mathrm{ad}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
<math>~\equiv</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>\frac{1}{(5-n)} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2 \, ,</math>
<math>~\frac{R_\mathrm{eq}}{R_\mathrm{ad}} \, ,</math>
   </td>
   </td>
</tr>
</tr>
Line 2,266: Line 2,242:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\mathcal{B}</math>
<math>~\Pi_\mathrm{ad}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
<math>~\equiv</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~\frac{P_\mathrm{e}}{P_\mathrm{ad}} \, .</math>
\frac{4\pi}{3}
\biggl( \frac{\bar{P}}{P_\mathrm{norm}} \biggr)\chi^{3(n+1)/n}_\mathrm{eq} \, ,
</math>
   </td>
   </td>
</tr>
</tr>
 
</table>
</div>
By demanding that the leading coefficients of both terms on the right-hand-side of the expression are simultaneously unity &#8212; that is, by demanding that,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\mathcal{D}</math>
<math>~\biggl(\frac{3}{4\pi}\biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
\biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{3\gamma_g}
\frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_M^{\gamma_g}}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,287: Line 2,266:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~1 \, ,</math>
\biggl( \frac{4\pi}{3} \biggr) \frac{P_e}{P_\mathrm{norm}} \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
 
and,
=====Strategy=====
 
Generic setup:
* Choose the polytropic index, <math>~n</math>, which also sets the value of the adiabatic index, <math>~\gamma=(n+1)/n</math>.
* Fix <math>~M_\mathrm{tot}</math> and <math>~K</math>, so that the radial and pressure normalizations are fixed; specifically,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~R_\mathrm{norm}^{n-3} = \biggl( \frac{G}{K} \biggr)^n M_\mathrm{tot}^{n-1} </math>
<math>~\frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2}
\biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{4}
\frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_M^2} </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
&nbsp;&nbsp;&nbsp;&nbsp; and &nbsp;&nbsp;&nbsp;&nbsp;
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~P_\mathrm{norm}^{(n-3)} = K^{4n} (G^3 M_\mathrm{tot}^2)^{-(n+1)} \, .</math>
<math>~1 \, ,</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
* Fix <math>~M_\mathrm{limit}</math>, and let it be the normalization mass; that is, set <math>~M_\mathrm{limit} = M_\mathrm{tot}</math>.
we obtain the expressions for <math>~R_\mathrm{ad}/R_\mathrm{norm}</math> and <math>~P_\mathrm{ad}/P_\mathrm{norm}</math> as shown in the following table.
* As a result of the above choices, the value of <math>~\mathcal{A}</math> is set, and fixed; specifically,
<div align="center">
<div align="center">
<math>~A = \frac{1}{(5-n)} \, .</math>
<table border="1" align="center" cellpadding="5">
</div>
<tr><th align="center" colspan="1">
Renormalization for Adiabatic (''ad'') Systems
</th></tr>
<tr><td align="center">


'''<font color="red">Case I:</font>''' 
* Fix <math>~\mathcal{D}</math>, which fixes the external pressure; specifically,
<div align="center">
<math>~P_e = \frac{3}{4\pi} \cdot \mathcal{D} P_\mathrm{norm} \, .</math>
</div>
* Choose a variety of values of the remaining coefficient, <math>~\mathcal{B}</math>; then, for each value, plot <math>\mathfrak{G}^*(\chi)</math> and locate one or more extrema along with the value of <math>~\chi_\mathrm{eq}</math> that is associated with each free energy extremum.  This identifies the equilibrium value of the mean pressure inside the pressure-truncated polytrope via the expression,
<div align="center">
<math>~ \bar{P} = \biggl(\frac{3}{4\pi} \biggr) P_\mathrm{norm}~\mathcal{B} ~\chi^{-3(n+1)/n}_\mathrm{eq}  \, .</math>
</div>
* In order to check whether we've identified the correct value of <math>~\chi_\mathrm{eq}</math>, we have to relate it to the radial coordinate, <math>~\xi_e</math>, used in the analytic solution of the Lane-Emden equation.  As has been explained in our [[User:Tohline/SSC/Structure/Polytropes#Polytropic_Spheres|discussion of detailed force-balanced models of polytropes]], generically,
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~R_\mathrm{eq} </math>
<math>~\frac{R_\mathrm{ad}}{R_\mathrm{norm}}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
<math>~\equiv</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~a_n \xi_e \, ,</math>&nbsp; &nbsp; &nbsp; &nbsp; where,
<math>~\biggl[ \frac{1}{5} \biggl( \frac{4\pi}{3} \biggr)^{\gamma_g-1} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2-\gamma_g}
\frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_A \cdot \tilde\mathfrak{f}_M^{2-\gamma_g}} \biggr]^{1/(4-3\gamma_g)} </math>
   </td>
   </td>
</tr>
</tr>
Line 2,347: Line 2,313:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~a_\mathrm{n} </math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~\equiv</math>
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~
<math>~
\biggl[\frac{1}{4\pi G}~ \biggl( \frac{H_c}{\rho_c} \biggr)\biggr]^{1/2}
\biggl[
=
\frac{1}{5^n} \biggl( \frac{4\pi}{3}\biggr)\biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{n-1}
\biggl[ \frac{(n+1)K}{4\pi G} \cdot \rho_c^{(1-n)/n}\biggr]^{1/2}
\frac{\tilde\mathfrak{f}_W^n}{\tilde\mathfrak{f}_A^n \cdot \tilde\mathfrak{f}_M^{n-1}}
\biggr]^{1/(n-3)}
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\Rightarrow ~~~ \biggl( \frac{a_n}{R_\mathrm{norm}} \biggr)^2</math>
<math>~\frac{P_\mathrm{ad}}{P_\mathrm{norm}}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
<math>~\equiv</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\biggl[ \frac{(n+1) K }{4\pi G} \biggr] \rho_c^{(1-n)/n} \cdot \frac{1}{R_\mathrm{norm}^2}</math>
<math>~ \biggl[ \tilde\mathfrak{f}_A^4 \cdot \biggl( \frac{3\cdot  5^3}{4\pi} \cdot
\frac{\tilde\mathfrak{f}_M^2}{\tilde\mathfrak{f}_W^3} \biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2\gamma_g} \biggr]^{1/(4-3\gamma)} </math>
   </td>
   </td>
</tr>
</tr>
Line 2,386: Line 2,349:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\biggl[ \frac{(n+1) K }{4\pi G} \biggr] \biggl( \frac{\rho_c}{\bar\rho} \biggr)^{(1-n)/n}  
<math>~
\biggl( \frac{3M_\mathrm{limit}}{4\pi R_\mathrm{eq}^3} \biggr)^{(1-n)/n}  
\biggl[
\cdot \frac{1}{R_\mathrm{norm}^2}  
\tilde\mathfrak{f}_A^{4n} \biggl(\frac{3\cdot 5^3}{4\pi} \biggr)^{n+1} \biggl( \frac{\tilde\mathfrak{f}_M^2}{\tilde\mathfrak{f}_w^3} \biggr)^{n+1}
\biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2(n+1)}
\biggr]^{1/(n-3)}
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>


</td>
</tr>
</table>
</div>
Using these new normalizations, we arrive at the desired, concise virial equilibrium relation, namely,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\Pi_\mathrm{ad} = \Chi_\mathrm{ad}^{-3\gamma_g} - \Chi_\mathrm{ad}^{-4}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <math>\Leftrightarrow</math>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\biggl[ \frac{(n+1) K }{4\pi G} \biggr] \biggl( \frac{\rho_c}{\bar\rho} \biggr)^{(1-n)/n}
<math>~ \Pi_\mathrm{ad} = \Chi_\mathrm{ad}^{-3(n+1)/n} - \Chi_\mathrm{ad}^{-4}</math>
\biggl( \frac{3M_\mathrm{tot}}{4\pi} \biggr)^{(1-n)/n} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{(1-n)/n} \chi_\mathrm{eq}^{3(n-1)/n}
\cdot R_\mathrm{norm}^{(n-3)/n}
</math>
   </td>
   </td>
</tr>
</tr>
 
</table>
</div>
or,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~~\Chi_\mathrm{ad}^{4-3\gamma_g} - \Pi_\mathrm{ad} \Chi_\mathrm{ad}^4 = 1</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <math>\Leftrightarrow</math>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{(n+1) }{4\pi }
<math>~\Chi_\mathrm{ad}^{(n-3)/n} - \Pi_\mathrm{ad} \Chi_\mathrm{ad}^4 = 1 \, .</math>
\biggl[ \frac{3}{4\pi}\biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\tilde\mathfrak{f}_M} \biggr]^{(1-n)/n}  
\chi_\mathrm{eq}^{3(n-1)/n} \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
Hence,
 
=====In Terms of Free-Energy Coefficients=====
 
Referring back to relations between our free-energy coefficients, as [[User:Tohline/SSC/Virial/PolytropesEmbedded/FirstEffortAgain#ABratios|presented earlier]], we note that,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
Line 2,431: Line 2,405:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\xi_e^2</math>
<math>~\frac{R_\mathrm{ad}}{R_\mathrm{norm}}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,437: Line 2,411:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\biggl( \frac{R_\mathrm{eq}}{a_n} \biggr)^2 = \chi_\mathrm{eq}^2 \biggl( \frac{a_n}{R_\mathrm{norm}} \biggr)^{-2}</math>
<math>~\biggl( \frac{\mathcal{A}}{\mathcal{B}}\biggr)^{n/(n-3)} \, ,</math>
   </td>
   </td>
</tr>
</tr>
Line 2,443: Line 2,417:
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\frac{P_\mathrm{ad}}{P_\mathrm{norm}}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,449: Line 2,423:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\chi_\mathrm{eq}^2 \biggl\{
<math>~\frac{3}{4\pi} \biggl[ \frac{\mathcal{B}^{4n}}{\mathcal{A}^{3(n+1)}} \biggr]^{1/(n-3)} \, .</math>
\frac{4\pi }{(n+1) }
\biggl[ \frac{3}{4\pi}\biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\tilde\mathfrak{f}_M} \biggr]^{(n-1)/n}  
\chi_\mathrm{eq}^{3(1-n)/n}
\biggr\}</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
Hence, we can write,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\Chi_\mathrm{ad}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,465: Line 2,440:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{4\pi }{(n+1) }
<math>~\chi_\mathrm{eq} ~\biggl( \frac{\mathcal{B}}{\mathcal{A}}\biggr)^{n/(n-3)} \, ,</math>
\biggl[ \frac{3}{4\pi}\biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\tilde\mathfrak{f}_M} \biggr]^{(n-1)/n}
\chi_\mathrm{eq}^{(3-n)/n} \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
But, from above, we also know that,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\frac{3}{4\pi}\biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\tilde\mathfrak{f}_M} </math>
<math>~\Pi_\mathrm{ad}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,485: Line 2,452:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\biggl[ \frac{3\mathcal{B}}{4\pi} \cdot \frac{1}{\tilde\mathfrak{f}_A} \biggr]^{n/(n+1)} \, ,</math>
<math>~\mathcal{D} ~\biggl[ \frac{\mathcal{A}^{3(n+1)}}{\mathcal{B}^{4n}} \biggr]^{1/(n-3)} \, .</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
where,
 
 
 
=====In Terms of Horedt's Equilibrium Parameters=====
For later use it is also worth developing expressions for both <math>~\Chi_\mathrm{ad}</math> and <math>~\Pi_\mathrm{ad}</math> that are in terms of our structural form factors and Horedt's two dimensionless functions, <math>~r_a</math> and <math>~p_a</math>.  (Adopting a unified notation, we will set <math>~\gamma_g \rightarrow (n+1)/n</math>.)
 
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
Line 2,496: Line 2,468:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\tilde\mathfrak{f}_A  = \frac{\bar{P}}{P_c}</math>
<math>~\Chi_\mathrm{ad} \equiv \frac{R_\mathrm{eq}}{R_\mathrm{ad}}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,502: Line 2,474:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~\frac{R_\mathrm{eq}}{R_\mathrm{Hoerdt}} \cdot \frac{R_\mathrm{Hoerdt}}{R_\mathrm{norm}} \cdot \frac{R_\mathrm{norm}}{R_\mathrm{ad}}</math>
\frac{3(n+1) }{(5-n)} ~\biggl( \Theta^' \biggr)^2_{\tilde\xi}  + \tilde\Theta^{n+1} \, ,
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
Hence we can write,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\xi_e^2</math>
&nbsp; 
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,522: Line 2,486:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{4\pi }{(n+1) }
<math>~
\biggl[ \frac{3\mathcal{B}}{4\pi} \cdot \frac{1}{\tilde\mathfrak{f}_A} \biggr]^{(n-1)/(n+1)}  
r_a \cdot \biggl[ \frac{4\pi}{(n+1)^n} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)^{n-1} \biggr]^{1/(n-3)} \cdot
\chi_\mathrm{eq}^{(3-n)/n} \, ,
\biggl[ 5^n \biggl( \frac{3}{4\pi} \biggr) \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)^{1-n}
\frac{\tilde\mathfrak{f}_A^n}{\tilde\mathfrak{f}_W^n \cdot \tilde\mathfrak{f}_M^{1-n}}
\biggr]^{1/(n-3)}
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>
or,
<div align="center">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\xi_e^2 \biggl[ \frac{3(n+1) }{(5-n)} ~\biggl( \Theta^' \biggr)^2_{\tilde\xi} + \tilde\Theta^{n+1} \biggr]^{(n-1)/(n+1)}</math>
<math>~\Rightarrow~~~\Chi_\mathrm{ad}^{n-3} </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,543: Line 2,503:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{4\pi }{(n+1) }
<math>~
\biggl[ \frac{3\mathcal{B}}{4\pi} \biggr]^{(n-1)/(n+1)}
3 r_a^{n-3} \cdot \biggl[ \frac{5}{(n+1)} \cdot
\chi_\mathrm{eq}^{(3-n)/n} \, .
\frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_W} \biggr]^n \tilde\mathfrak{f}_M^{n-1} \, .
</math>
</math>
   </td>
   </td>
Line 2,551: Line 2,511:
</table>
</table>
</div>
</div>
This last expression may be useful because the numerical value of the right-hand-side will be known once an extremum of a free-energy plot has been identified, while the function on the left-hand side can be evaluated separately, from knowledge of the internal structure of detailed force-balanced, ''isolated'' polytropes.


=====Strategy2=====
And,
* Pick the desired polytropic index, <math>~n</math>, and a radial coordinate within the isolated polytropic model, <math>~\tilde\xi \leq \xi_1</math>, that will serve as the truncated edge of the embedded polytrope.
* Knowledge of the isolated polytrope's internal structure will give the value of the Lane-Emden function, <math>~\tilde\theta</math>, and its radial derivative, <math>~{\tilde\theta'}</math>, at this truncated edge of the structure.
* According to [http://adsabs.harvard.edu/abs/1970MNRAS.151...81H Horedt (1970)] &#8212; see our [[User:Tohline/SSC/Structure/PolytropesEmbedded#Horedt.27s_Presentation|accompanying discussion of detailed force-balanced models]] &#8212; the physical radius and external pressure that corresponds to this choice of the truncated edge is given by the expressions,
<div align="center">
<div align="center">
<table border="0" cellpadding="3">
<table border="0" cellpadding="5" align="center">


<tr>
<tr>
   <td align="right">
   <td align="right">
<math>
<math>~\Pi_\mathrm{ad} \equiv \frac{P_e}{P_\mathrm{ad}}</math>
~\frac{R_\mathrm{eq}}{R_\mathrm{norm}} = r_a \biggl( \frac{R_\mathrm{Horedt}}{R_\mathrm{norm}} \biggr)
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=~</math>
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~\frac{P_e}{P_\mathrm{Hoerdt}} \cdot \frac{P_\mathrm{Hoerdt}}{P_\mathrm{norm}} \cdot \frac{P_\mathrm{norm}}{P_\mathrm{ad}}</math>
\tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)} \biggl[ \frac{4\pi}{(n+1)^n} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{n-1} \biggr]^{1/(n-3)} \, ,
</math>
   </td>
   </td>
</tr>
</tr>
Line 2,578: Line 2,530:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>
&nbsp;
~\frac{P_e}{P_\mathrm{norm}} = p_a \biggl( \frac{P_\mathrm{Horedt}}{P_\mathrm{norm}} \biggr)
</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=~</math>
<math>~=</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~
\tilde\theta_n^{n+1}( -\tilde\xi^2 \tilde\theta' )^{2(n+1)/(n-3)} \biggl[ \frac{(n+1)^3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2} \biggr]^{(n+1)/(n-3)}  \, .
p_a \cdot \biggl[ \frac{(n+1)^3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2}\biggr]^{(n+1)/(n-3)} \cdot
</math>
\biggl[ \tilde\mathfrak{f}_A^{-4n} \cdot \biggl( \frac{4\pi}{3\cdot  5^3} \cdot
\frac{\tilde\mathfrak{f}_W^3}{\tilde\mathfrak{f}_M^2} \biggr)^{(n+1)} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2(n+1)}  
\biggr]^{1/(n-3)}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\Rightarrow~~~\Pi_\mathrm{ad}^{n-3} </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
p_a^{n-3}~ \tilde\mathfrak{f}_A^{-4n} \cdot \biggl[
\frac{(n+1)^3}{3\cdot 5^3} \biggl( \frac{\tilde\mathfrak{f}_W^3}{\tilde\mathfrak{f}_M^2} \biggr)
\biggr]^{n+1} \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
 
Plugging in the expressions for <math>~r_a</math> and <math>~p_a</math>, as [[User:Tohline/SSC/Virial/PolytropesEmbedded/FirstEffortAgain#Contrast_with_Detailed_Force-Balanced_Solution|reprinted, for example, above]], along with our [[User:Tohline/SSC/Virial/PolytropesEmbedded/FirstEffortAgain#PTtable|deduced expressions for <math>~\mathfrak{f}_M</math> and <math>~\mathfrak{f}_A</math> (in terms of <math>~\mathfrak{f}_W</math>)]], these two relations become:
* Using the chosen value of <math>~\tilde\xi</math> and its associated function values, <math>~\tilde\theta</math> and <math>~\tilde\theta^'</math>, determine the values of the three relevant structural form factors via the following analytic relations:


<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\tilde\mathfrak{f}_M = \frac{\bar\rho}{\rho_c}</math>
<math>~\Chi_\mathrm{ad}^{n-3} </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,606: Line 2,575:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~ \biggl[ - \frac{3 \tilde\theta^'}{\tilde\xi} \biggr] \, ,</math>
<math>~
3 \biggl[ \tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)} \biggr]^{n-3} \cdot \biggl[ \frac{5}{(n+1)} \cdot
\frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_W} \biggr]^n \biggl[- \frac{3\tilde\theta^'}{\tilde\xi} \biggr]^{n-1}
</math>
   </td>
   </td>
</tr>
</tr>
Line 2,612: Line 2,584:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\tilde\mathfrak{f}_W </math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,618: Line 2,590:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{3^2\cdot 5}{5-n} \biggl[ \frac{\tilde\theta^'}{\tilde\xi} \biggr]^2 = \biggl( \frac{5}{5-n} \biggr) \tilde\mathfrak{f}_M^2 \, ,</math>
<math>~
\tilde\xi^{[(n-3)+2(1-n)-(n-1)]} \cdot \biggl[ \frac{3\cdot 5}{(n+1)} \cdot
\frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_W} \biggr]^n
</math>
   </td>
   </td>
</tr>
</tr>
Line 2,624: Line 2,599:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>\tilde\mathfrak{f}_A  = \frac{\bar{P}}{P_c}</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,630: Line 2,605:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~
\frac{3(n+1) }{(5-n)} ~( \tilde\theta^')^2  + \tilde\theta^{n+1} \, .
\biggl[ \frac{3\cdot 5}{(n+1)\tilde\xi^2} \cdot
\frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_W} \biggr]^n \, ;
</math>
</math>
   </td>
   </td>
Line 2,637: Line 2,613:
</table>
</table>
</div>
</div>
* Using these values of the structural form factors, determine the values of the three free-energy coefficients (set <math>~M_\mathrm{limi}/M_\mathrm{tot} = 1</math> for the time being) via the expressions:
and,
 
<div align="center">
<div align="center">
<table border="0" cellpadding="5">
<table border="0" cellpadding="5" align="center">
 
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\mathcal{A}_\mathrm{mod} \equiv (5-n)\mathcal{A}</math>
<math>~\Pi_\mathrm{ad}^{n-3} </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,648: Line 2,626:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>\frac{(5-n)}{5} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2} \frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_M^2}  
<math>~
= \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2} \, ,</math>
\biggl[ \tilde\theta_n^{n+1}( -\tilde\xi^2 \tilde\theta' )^{2(n+1)/(n-3)} \biggr]^{n-3}~ \tilde\mathfrak{f}_A^{-4n} \cdot \biggl[
\frac{(n+1)}{3\cdot  5} \cdot \tilde\mathfrak{f}_W \biggr]^{3(n+1)} \biggl( \frac{3}{\tilde\mathfrak{f}_M}\biggr)^{2(n+1)}
</math>
   </td>
   </td>
</tr>
</tr>
Line 2,655: Line 2,635:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\mathcal{B}_\mathrm{mod} \equiv (5-n)\mathcal{B}</math>
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,661: Line 2,641:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~
\biggl( \frac{3}{4\pi} \biggr)^{1/n}
\tilde\theta_n^{(n+1)(n-3)}( -\tilde\xi^2 \tilde\theta' )^{2(n+1)} ~ \tilde\mathfrak{f}_A^{-4n} \cdot \tilde\xi^{-6(n+1)} \biggl[
\biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\tilde\mathfrak{f}_M} \biggr]_\mathrm{eq}^{(n+1)/n}
\frac{(n+1)\tilde\xi^2}{3\cdot  5} \cdot \tilde\mathfrak{f}_W \biggr]^{3(n+1)} \tilde\xi^{2(n+1)} (-\tilde\theta^')^{-2(n+1)}
\cdot [(5-n)\tilde\mathfrak{f}_A]
</math>
</math>
   </td>
   </td>
Line 2,677: Line 2,656:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>
<math>~
\frac{4\pi}{3} \biggl( \frac{P_c}{P_\mathrm{norm}} \biggr) \chi_\mathrm{eq}^{3(n+1)/n}
\tilde\theta_n^{(n+1)(n-3)}~ \tilde\mathfrak{f}_A^{-4n} \cdot \biggl[
\cdot [(5-n)\tilde\mathfrak{f}_A]
\frac{(n+1)\tilde\xi^2}{3\cdot  5} \cdot \tilde\mathfrak{f}_W \biggr]^{3(n+1)} \, .  
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\mathcal{D}_\mathrm{mod} \equiv (5-n) \mathcal{D}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
\biggl( \frac{4\pi}{3} \biggr) (5-n) \frac{P_e}{P_\mathrm{norm}} \, .
</math>
</math>
   </td>
   </td>
Line 2,699: Line 2,664:
</table>
</table>
</div>
</div>
* Plot the following free-energy function and see if the value of <math>~\chi</math> associated with the extremum is equal to the dimensionless equilibrium radius, <math>~R_\mathrm{eq}/R_\mathrm{norm}</math>, as predicted by Hoerdt's expression, above:
 
=====Summary=====
If we define,  
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
Line 2,705: Line 2,672:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~(5-n)\mathfrak{G}^*</math>
<math>~a_\mathrm{ad}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
<math>~\equiv</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~-3\mathcal{A}_\mathrm{mod} \chi^{-1} -~ \frac{1}{(1-\gamma_g)} \mathcal{B}_\mathrm{mod} \chi^{3-3\gamma_g} +~ \mathcal{D}_\mathrm{mod}\chi^3</math>
<math>~\frac{(n+1)\tilde\xi^2 }{3\cdot 5} \cdot \mathfrak{f}_W \, ,</math> &nbsp;&nbsp;&nbsp; and,
   </td>
   </td>
</tr>
</tr>
Line 2,717: Line 2,684:
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~b_\mathrm{ad}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
<math>~\equiv</math>
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~-3\mathcal{A}_\mathrm{mod} \chi^{-1} +n\mathcal{B}_\mathrm{mod} \chi^{-3/n} +~ \mathcal{D}_\mathrm{mod}\chi^3 \, .</math>
<math>~\tilde\theta^{n+1} \, ,</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
* Virial equilbrium &#8212; that is, an extremum in the free energy function &#8212; occurs when <math>~\partial\mathfrak{G}^*/\partial\chi = 0</math>, that is, where,
in which case the [[User:Tohline/SSC/Virial/PolytropesEmbedded/FirstEffortAgain#PTtable|relationship between <math>~\mathfrak{f}_A</math> and <math>~\mathfrak{f}_A</math> for pressure-truncated polytropes]] can be rewritten as,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
Line 2,734: Line 2,701:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\mathcal{B}_\mathrm{mod} \chi_\mathrm{eq}^{(n-3)/n} - \mathcal{D}_\mathrm{mod}\chi_\mathrm{eq}^4</math>
<math>~\mathfrak{f}_A </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,740: Line 2,707:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\mathcal{A}_\mathrm{mod} \, .</math>
<math>~a_\mathrm{ad} + b_\mathrm{ad} \, .</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
 
In addition, the expressions for the dimensionless equilibrium radius and the dimensionless external pressure, as just derived, may be written as, respectively,
Note that if the coefficient, <math>~\mathcal{B}</math>, is written in terms of the normalized central pressure, the statement of virial equilibrium becomes,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="0" cellpadding="5" align="center">
Line 2,752: Line 2,718:
<tr>
<tr>
   <td align="right">
   <td align="right">
<math>~\mathcal{A}_\mathrm{mod} </math>
<math>~\Chi_\mathrm{ad}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,758: Line 2,724:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\biggl[ \frac{4\pi}{3}\biggl( \frac{P_c}{P_\mathrm{norm}} \biggr) \chi_\mathrm{eq}^{3(n+1)/n}
<math>~
\cdot [(5-n)\tilde\mathfrak{f}_A] \biggr] \chi_\mathrm{eq}^{(n-3)/n} - \frac{4\pi}{3} (5-n)\biggl( \frac{P_e}{P_\mathrm{norm}} \biggr) \chi_\mathrm{eq}^4</math>
\biggl[ 1 + \frac{b_\mathrm{ad}}{a_\mathrm{ad}} \biggr]^{n/(n-3)} \, ,
</math> &nbsp;&nbsp;&nbsp; and,
   </td>
   </td>
</tr>
</tr>
Line 2,765: Line 2,732:
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\Pi_\mathrm{ad} </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,771: Line 2,738:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{4\pi}{3}\chi_\mathrm{eq}^4 \biggl\{\biggl( \frac{P_c}{P_\mathrm{norm}} \biggr)
<math>~
\cdot (5-n)\tilde\mathfrak{f}_A  - (5-n)\biggl( \frac{P_e}{P_\mathrm{norm}} \biggr) \biggr\}
b_\mathrm{ad} \biggl[ \frac{a_\mathrm{ad}^{3(n+1)} }{( a_\mathrm{ad} + b_\mathrm{ad} )^{4n} } \biggr]^{1/(n-3)}
=
\frac{b_\mathrm{ad}}{a_\mathrm{ad}} \biggl[ 1 + \frac{b_\mathrm{ad}}{a_\mathrm{ad}} \biggr]^{-4n/(n-3)}
\, .
</math>
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</div>


Using these expressions, it is easy to demonstrate that the virial equilibrium relation is satisfied, namely,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
<tr>
   <td align="right">
   <td align="right">
&nbsp;
<math>~\Pi_\mathrm{ad} </math>
   </td>
   </td>
   <td align="center">
   <td align="center">
Line 2,785: Line 2,760:
   </td>
   </td>
   <td align="left">
   <td align="left">
<math>~\frac{4\pi}{3}\chi_\mathrm{eq}^4 \biggl\{\biggl( \frac{P_c}{P_\mathrm{norm}} \biggr)
<math>~\Chi_\mathrm{ad}^{-3(n+1)/n} - \Chi_\mathrm{ad}^{-4} \, .</math>
\cdot \biggl[ 3(n+1) (\tilde\theta^')^2 + (5-n)\tilde\theta^{n+1} \biggr]  - (5-n)\biggl( \frac{P_e}{P_\mathrm{norm}} \biggr) \biggr\} \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
But, in this situation, <math>~\tilde\theta^{n+1} = P_e/P_c</math>, so virial equilibrium implies,
 
====P-V Diagram====
 
For an arbitrary value of the adiabatic exponent, <math>~\gamma_g</math>, it isn't possible to invert this virial relation to obtain an analytic expression for <math>~\chi_\mathrm{ad}</math> as a function of <math>~\Pi_\mathrm{ad}</math>.  But, as written, the virial relation dictates the behavior of <math>~\Pi_\mathrm{ad}</math> as a function of <math>~\Chi_\mathrm{ad}</math>.  Figure 4 displays this <math>~\Pi_\mathrm{ad}(\chi_\mathrm{ad})</math> behavior for a number of different values of <math>~\gamma_g</math>.
 
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<table border="2" cellpadding="8">
 
<tr>
<tr>
   <td align="right">
   <td align="center" colspan="2">
<math>~\frac{3}{4\pi}\chi_\mathrm{eq}^{-4} \mathcal{A}_\mathrm{mod} </math>
'''Figure 4:''' <font color="darkblue">Equilibrium Adiabatic P-V Diagram </font>  
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\biggl( \frac{P_c}{P_\mathrm{norm}} \biggr)
\cdot \biggl[ 3(n+1) (\tilde\theta^')^2 + (5-n)\frac{P_e}{P_c} \biggr]  - (5-n)\biggl( \frac{P_e}{P_\mathrm{norm}} \biggr)
</math>
   </td>
   </td>
</tr>
</tr>
<tr>
<tr>
   <td align="right">
   <td valign="top" width=450 rowspan="1">
&nbsp;
The curves shown here, on the right, trace out the function,
  </td>
<div align="center">
  <td align="center">
<math>
<math>~=</math>
~\Pi_\mathrm{ad} = (\Chi_\mathrm{ad}^{4-3\gamma_g} - 1)/\Chi_\mathrm{ad}^4 \, ,
  </td>
  <td align="left">
<math>~3(n+1) (\tilde\theta^')^2\biggl( \frac{P_c}{P_\mathrm{norm}} \biggr)
</math>
</math>
</div>
for six different values of <math>~\gamma_g</math> &#8212; specifically, for <math>2, ~5/3, ~7/5, ~6/5, ~1, ~2/3</math>, as labeled &#8212;  and show the dimensionless external pressure, <math>~\Pi_\mathrm{ad}</math>, that is required to construct a nonrotating, self-gravitating, pressure-truncated adiabatic sphere with an equilibrium radius <math>~\Chi_\mathrm{ad}</math>.  The solid red curve identifies the behavior of an isothermal <math>~(\gamma_g=1)</math> system.  The mathematical solution becomes unphysical wherever the pressure becomes negative.
</td>
  <td align="center" bgcolor="white">
[[File:AdabaticBoundedSpheres_Virial.jpg|450px|center|Equilibrium Adiabatic P-R Diagram]]
   </td>
   </td>
</tr>
</tr>
</table>
</div>


<tr>
 
  <td align="right">
For physically relevant solutions, both <math>~\Chi_\mathrm{ad}</math> and <math>~\Pi_\mathrm{ad}</math> must be nonnegative.  Hence, as is illustrated by the curves in Figure 4, the physically allowable range of equilibrium radii is,
<math>~\Rightarrow~~~\frac{P_c}{P_\mathrm{norm}} \biggl( \frac{R_\mathrm{eq}}{R_\mathrm{norm}\biggr)^4 \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2}
<div align="center">
<math>
1 \le \Chi_\mathrm{ad} \le \infty \, ~~~~~\mathrm{for}~ \gamma_g < 4/3 \, ;
</math>
</math>
  </td>
 
  <td align="center">
<math>
<math>~=</math>
0 < \Chi_\mathrm{ad} \le 1 \, ~~~~~~\mathrm{for}~ \gamma_g > 4/3 \, .
  </td>
  <td align="left">
<math>~\biggl[ 4\pi(n+1) (\tilde\theta^')^2 \biggr]^{-1}
</math>
</math>
  </td>
</div>
</tr>


<tr>
Each of the <math>~\Pi_\mathrm{ad}(\Chi_\mathrm{ad})</math> curves drawn in Figure 4 exhibits an extremum.  In each case this extremum occurs at a configuration radius, <math>~\Chi_\mathrm{extreme}</math>, given by,
  <td align="right">
<div align="center">
<math>~\Rightarrow~~~\frac{P_c R_\mathrm{eq}^4}{GM_\mathrm{limit}^2}
<math>
</math>
\frac{\partial\Pi_\mathrm{ad}}{\partial\Chi_\mathrm{ad}} = 0 \, ,
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\frac{1}{4\pi(n+1) (\tilde\theta^')^2} \, .
</math>
</math>
  </td>
</tr>
</table>
</div>
</div>
 
that is, where,
=====Compare With Detailed Force Balanced Solution=====
In a [[User:Tohline/SSC/Structure/PolytropesEmbedded#.3D_1_Polytrope|separate discussion]], we presented the detailed force-balanced model of an <math>~n=1</math> polytrope that is embedded in an external medium.  We showed that, for an applied external pressure given by,
<div align="center">
<div align="center">
<math>\frac{P_e}{P_\mathrm{norm}} = \frac{\pi}{2} \biggl[ \frac{\sin\xi_e}{\xi_e(\sin\xi_e - \xi_e \cos\xi_e )} \biggr]^2 \, ,</math>  
<math>
4 - 3\gamma_g \Chi_\mathrm{ad}^{4-3\gamma_g} = 0 ~~~~\Rightarrow ~~~~~ \Chi_\mathrm{extreme} = \biggl[ \frac{4}{3\gamma_g} \biggr]^{1/(4-3\gamma_g)} \, .
</math>
</div>
</div>
the associated equilibrium radius of the pressure-confined configuration is,
For each value of <math>~\gamma_g</math>, the corresponding dimensionless pressure is,
<div align="center">
<div align="center">
<math>
<math>
R_\mathrm{eq} = \xi_e a_\mathrm{n=1} = \biggl[ \frac{K}{2\pi G} \biggr]^{1/2} \xi_e \, .
~\Pi_\mathrm{extreme} = \biggl(\frac{4}{3\gamma} - 1 \biggr) \biggl[ \frac{3\gamma_g}{4} \biggr]^{4/(4-3\gamma_g)} \, .
</math>
</math>
</div>
</div>
Flipping this around, after we use a plot of the free-energy expression to identify the equilibrium radius, <math>~\chi_\mathrm{eq}</math>, the corresponding dimensionless radius as used in the Lane-Emden equation should be,
In terms of the polytropic index, the equivalent limiting expressions are,
<div align="center">
<div align="center">
<table border="0" cellpadding="5">
<table border="0" cellpadding="5">
<tr>
<tr>
   <td align="right">
   <td align="center">
<math>~\xi_e</math>
<math>~\Chi_\mathrm{extreme} = \biggl[ \frac{4n}{3(n+1)} \biggr]^{n/(n-3)}</math>
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; and &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;  
  </td>
  <td align="left">
<math>
\biggl[ \frac{2\pi G}{K} \biggr]^{1/2} R_\mathrm{norm} \cdot \chi_\mathrm{eq}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
   </td>
   </td>
   <td align="center">
   <td align="center">
<math>~=</math>
<math>~\Pi_\mathrm{extreme}^{(n-3)} = (4n)^{-4n} (n-3)^{n-3} [3(n+1)]^{3(n+1)} \, .</math>
  </td>
  <td align="left">
<math>~(2\pi)^{1/2} \chi_\mathrm{eq} \, .
</math>
   </td>
   </td>
</tr>
</tr>
</table>
</table>
</div>
</div>
Keep in mind that, for an [[User:Tohline/SSC/Structure/Polytropes#.3D_1_Polytrope|isolated <math>~n=1</math> polytrope]], the (zero pressure) surface is identified by <math>~\xi_1 = \pi</math>. Hence we should expect free-energy extrema to occur at values of <math>~\chi_\mathrm{eq} \le \pi/2</math>.
(In a [[User:Tohline/SSC/Virial/PolytropesEmbedded/SecondEffortAgain#Stability|separate, related discussion of the free-energy function]], we demonstrate that this "extremum" also serves as a dividing line between dynamically stable and unstable models along a given curve.)


====Renormalization====


=====Grunt Work=====
In examining the group of plotted curves, notice that, for <math>~\gamma_g > 4/3</math>, an equilibrium configuration with a positive radius can be constructed for all physically realistic &#8212; that is, for all positive &#8212; values of <math>~\Pi_\mathrm{ad}</math>.  Also, consistent with the behavior of the curves shown in Figure 4, the extremum arises in the regime of physically relevant &#8212; ''i.e.,'' positive &#8212; pressures only for values of <math>~\gamma_g < 4/3</math>; and in each case it represents a ''maximum'' limiting pressure.
 
 
{{LSU_WorkInProgress}}
 
====Maximum Mass====


Returning to the dimensionless form of the virial expression and multiplying through by <math>~[-\chi_\mathrm{eq}/(3D)]</math>, we obtain,
=====<math>n=5</math> Polytropic=====
When <math>~\gamma_a = 6/5</math> &#8212; which corresponds to an <math>~n=5</math> polytropic configuration &#8212; we obtain,
<div align="center">
<div align="center">
<math>
<math>
\chi_\mathrm{eq}^4 = \frac{B}{D} \chi_\mathrm{eq}^{4-3\gamma_g} - \frac{A}{D} \, ,
~\Pi_\mathrm{max} = \Pi_\mathrm{ad}\biggr|_\mathrm{extreme}^{(\gamma_g = 6/5)}  
= \biggl( \frac{3^{18}}{2^{10}\cdot 5^{10}} \biggr) \, ,
</math>
</math>
</div>
</div>
or, after plugging in [[User:Tohline/SphericallySymmetricConfigurations/Virial#Gathering_it_all_Together|definitions of the coefficients]], <math>~A</math>, <math>~B</math>, and <math>~D</math>, and rewriting <math>~\chi_\mathrm{eq}</math> explicitly as <math>~R_\mathrm{eq}/R_\mathrm{norm}</math>,
which corresponds to a maximum mass for pressure-bounded <math>~n=5</math> polytropic configurations of,
<div align="center">
<div align="center">
<table border="0" cellpadding="5" align="center">
<math>~M_\mathrm{max} = \Pi_\mathrm{max}^{1/2}  \biggl(\frac{3\cdot 5^3}{2^2\pi} \biggr)^{1/2} \biggl( \frac{\bar{c_s}^8}{G^3 P_e} \biggr)^{1/2}
<tr>
= \biggl(\frac{3^{19}}{2^{12}\cdot 5^{7}\pi} \biggr)^{1/2} \biggl( \frac{\bar{c_s}^8}{G^3 P_e} \biggr)^{1/2} \, .</math>
  <td align="right">
</div>
<math>~\biggl( \frac{R_\mathrm{eq}}{R_\mathrm{norm}} \biggr)^4  </math>
This result can be compared to [[User:Tohline/SSC/Structure/LimitingMasses#Bounded_Isothermal_Sphere_.26_Bonnor-Ebert_Mass|other determinations of the Bonnor-Ebert mass limit]].
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
\biggl(\frac{3}{4\pi}\biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
\biggl( \frac{P_e}{P_\mathrm{norm}} \biggr)^{-1} \frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_M^{\gamma_g}}
\biggl( \frac{R_\mathrm{eq}}{R_\mathrm{norm}} \biggr)^{4-3\gamma_g} -  
\frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2} \biggl( \frac{P_e}{P_\mathrm{norm}} \biggr)^{-1}
\frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_M^2} \, .</math>
  </td>
</tr>
</table>
</div>
This relation can be written in a more physically concise form, as follows.  First, normalize <math>~P_e</math> to a new pressure scale &#8212; call it <math>~P_\mathrm{ad}</math> &#8212; and multiply through by <math>~(R_\mathrm{norm}/R_\mathrm{ad})^4</math> in order to normalizing <math>~R_\mathrm{eq}</math> to a new length scale,<math>~R_\mathrm{ad}</math>:
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\biggl( \frac{R_\mathrm{eq}}{R_\mathrm{ad}} \biggr)^4  </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
\biggl(\frac{3}{4\pi}\biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
\biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{P_e}{P_\mathrm{ad}} \biggr)^{-1} \frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_M^{\gamma_g}}
\biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{3\gamma_g}\biggl( \frac{R_\mathrm{eq}}{R_\mathrm{ad}} \biggr)^{4-3\gamma_g}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
&nbsp;
  </td>
  <td align="left">
<math>
~-
\frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2} \biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr)
\frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_M^2} \biggl( \frac{P_e}{P_\mathrm{ad}} \biggr)^{-1} \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{4} \, ,
</math>
  </td>
</tr>
</table>
</div>
or,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\chi_\mathrm{ad}^4  </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
\biggl(\frac{3}{4\pi}\biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
\biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{3\gamma_g}
\frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_M^{\gamma_g}}\cdot \frac{\chi_\mathrm{ad}^{4-3\gamma_g} }{\Pi_\mathrm{ad}} -
\frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2}
\biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{4}
\frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_M^2} \cdot \frac{1}{\Pi_\mathrm{ad}}  \, ,</math>
  </td>
</tr>
</table>
</div>
where,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\chi_\mathrm{ad}</math>
  </td>
  <td align="center">
<math>~\equiv</math>
  </td>
  <td align="left">
<math>~\frac{R_\mathrm{eq}}{R_\mathrm{ad}} \, ,</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\Pi_\mathrm{ad}</math>
  </td>
  <td align="center">
<math>~\equiv</math>
  </td>
  <td align="left">
<math>~\frac{P_\mathrm{e}}{P_\mathrm{ad}} \, .</math>
  </td>
</tr>
</table>
</div>
By demanding that the leading coefficients of both terms on the right-hand-side of the expression are simultaneously unity &#8212; that is, by demanding that,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\biggl(\frac{3}{4\pi}\biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g}
\biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{3\gamma_g}
\frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_M^{\gamma_g}}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~1 \, ,</math>
  </td>
</tr>
</table>
</div>
and,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2}
\biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{4}
\frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_M^2} </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~1 \, ,</math>
  </td>
</tr>
</table>
</div>
we obtain the expressions for <math>~R_\mathrm{ad}/R_\mathrm{norm}</math> and <math>~P_\mathrm{ad}/P_\mathrm{norm}</math> as shown in the following table.
<div align="center">
<table border="1" align="center" cellpadding="5">
<tr><th align="center" colspan="1">
Renormalization for Adiabatic (''ad'') Systems
</th></tr>
<tr><td align="center">
 
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\frac{R_\mathrm{ad}}{R_\mathrm{norm}}</math>
  </td>
  <td align="center">
<math>~\equiv</math>
  </td>
  <td align="left">
<math>~\biggl[ \frac{1}{5} \biggl( \frac{4\pi}{3} \biggr)^{\gamma_g-1} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2-\gamma_g}
\frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_A \cdot \tilde\mathfrak{f}_M^{2-\gamma_g}} \biggr]^{1/(4-3\gamma_g)} </math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\biggl[
\frac{1}{5^n} \biggl( \frac{4\pi}{3}\biggr)\biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{n-1}
\frac{\tilde\mathfrak{f}_W^n}{\tilde\mathfrak{f}_A^n \cdot \tilde\mathfrak{f}_M^{n-1}}
\biggr]^{1/(n-3)}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\frac{P_\mathrm{ad}}{P_\mathrm{norm}}</math>
  </td>
  <td align="center">
<math>~\equiv</math>
  </td>
  <td align="left">
<math>~ \biggl[ \tilde\mathfrak{f}_A^4 \cdot \biggl( \frac{3\cdot  5^3}{4\pi} \cdot
\frac{\tilde\mathfrak{f}_M^2}{\tilde\mathfrak{f}_W^3} \biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2\gamma_g} \biggr]^{1/(4-3\gamma)}  </math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\biggl[
\tilde\mathfrak{f}_A^{4n} \biggl(\frac{3\cdot 5^3}{4\pi} \biggr)^{n+1} \biggl( \frac{\tilde\mathfrak{f}_M^2}{\tilde\mathfrak{f}_w^3} \biggr)^{n+1}
\biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2(n+1)}
\biggr]^{1/(n-3)}
</math>
  </td>
</tr>
</table>
 
</td>
</tr>
</table>
</div>
Using these new normalizations, we arrive at the desired, concise virial equilibrium relation, namely,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\Pi_\mathrm{ad} </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\chi_\mathrm{ad}^{-3\gamma_g} - \chi_\mathrm{ad}^{-4} \, ,</math>
  </td>
</tr>
</table>
</div>
or,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\chi_\mathrm{ad}^{4-3\gamma_g} - \Pi_\mathrm{ad} \chi_\mathrm{ad}^4</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~1 \, .</math>
  </td>
</tr>
</table>
</div>
 
 
For the sake of completeness, we should develop expressions for both <math>~\chi_\mathrm{ad}</math> and <math>~\Pi_\mathrm{ad}</math> that are entirely in terms of the Lane-Emden function, <math>~\tilde\theta</math>, its derivative, <math>~\tilde\theta'</math>, and the associated dimensionless radial coordinate, <math>\tilde\xi</math>, at which the function and its derivative are to be evaluated.  (Adopting a unified notation, we will set <math>~\gamma_g \rightarrow (n+1)/n</math>.)
 
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\chi_\mathrm{ad} \equiv \frac{R_\mathrm{eq}}{R_\mathrm{ad}}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\frac{R_\mathrm{eq}}{R_\mathrm{Hoerdt}} \cdot \frac{R_\mathrm{Hoerdt}}{R_\mathrm{norm}} \cdot \frac{R_\mathrm{norm}}{R_\mathrm{ad}}</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp; 
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
r_a \cdot \biggl[ \frac{4\pi}{(n+1)^n} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)^{n-1} \biggr]^{1/(n-3)} \cdot
\biggl[ 5^n \biggl( \frac{3}{4\pi} \biggr) \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)^{1-n}
\frac{\tilde\mathfrak{f}_A^n}{\tilde\mathfrak{f}_W^n \cdot \tilde\mathfrak{f}_M^{1-n}}
\biggr]^{1/(n-3)}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\Rightarrow~~~\chi_\mathrm{ad}^{n-3} </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
3 r_a^{n-3} \cdot \biggl[ \frac{5}{(n+1)} \cdot
\frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_W} \biggr]^n \tilde\mathfrak{f}_M^{n-1} \, .
</math>
  </td>
</tr>
</table>
</div>
 
Inserting the functional expressions for Hoerdt's <math>~r_a</math> and our structural form factors, <math>\tilde\mathfrak{f}_i</math>, gives,
 
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\chi_\mathrm{ad}^{n-3}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
3 \tilde\mathfrak{f}_A^n \biggl[ \tilde\xi^{n-3} (-\tilde\xi^2 \tilde\theta')^{1-n} \biggr]
\biggl[ \frac{5}{(n+1)}  \cdot \frac{(5-n)}{5\cdot 3^2} \biggl( - \frac{\tilde\xi}{\tilde\theta'} \biggr)^2\biggr]^n \biggl[- \frac{3 \tilde\theta'}{\tilde\xi} \biggr]^{n-1}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\biggl[ \frac{(5-n)}{3(n+1)} \cdot \frac{\tilde\mathfrak{f}_A}{(-\tilde\theta')^2}\biggr]^n 
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\Rightarrow ~~~~ \chi_\mathrm{ad}^{(n-3)/n}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\frac{(5-n)}{3(n+1)} \cdot (-\tilde\theta')^{-2} \biggl[ \frac{3(n+1)}{(5-n)} (-\tilde\theta')^2 + \theta^{n+1} \biggr]
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~1 +
\frac{(5-n)}{3(n+1)} \cdot \frac{\tilde\theta^{n+1}}{(-\tilde\theta')^2} \, .
</math>
  </td>
</tr>
</table>
</div>
And,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\Pi_\mathrm{ad} \equiv \frac{P_e}{P_\mathrm{ad}}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\frac{P_e}{P_\mathrm{Hoerdt}} \cdot \frac{P_\mathrm{Hoerdt}}{P_\mathrm{norm}} \cdot \frac{P_\mathrm{norm}}{P_\mathrm{ad}}</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
p_a \cdot \biggl[ \frac{(n+1)^3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2}\biggr]^{(n+1)/(n-3)} \cdot
\biggl[ \tilde\mathfrak{f}_A^{-4n} \cdot \biggl( \frac{4\pi}{3\cdot  5^3} \cdot
\frac{\tilde\mathfrak{f}_W^3}{\tilde\mathfrak{f}_M^2} \biggr)^{(n+1)} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2(n+1)}
\biggr]^{1/(n-3)}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\Rightarrow~~~\Pi_\mathrm{ad}^{n-3} </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
p_a^{n-3}~ \tilde\mathfrak{f}_A^{-4n} \cdot \biggl[
\frac{(n+1)^3}{3\cdot  5^3} \biggl( \frac{\tilde\mathfrak{f}_W^3}{\tilde\mathfrak{f}_M^2} \biggr)
\biggr]^{n+1} \, .
</math>
  </td>
</tr>
</table>
</div>
 
Inserting the functional expressions for Hoerdt's <math>~p_a</math> and our structural form factors, <math>\tilde\mathfrak{f}_i</math>, gives,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\Pi_\mathrm{ad}^{n-3} </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\tilde\mathfrak{f}_A^{-4n} ~[  \tilde\theta^{n+1}( -\tilde\xi^2 \tilde\theta' )^{2(n+1)/(n-3)}  ]^{n-3}  \cdot \biggl[
\frac{(n+1)^3}{3\cdot  5^3}\biggr]^{n+1} 
\biggl[ \frac{3^2\cdot 5}{5-n} \biggl( \frac{\tilde\theta^'}{\tilde\xi} \biggr)^2 \biggr]^{3(n+1)}
\bigg( - \frac{3\tilde\theta^'}{\tilde\xi} \biggr)^{-2(n+1)}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\tilde\mathfrak{f}_A^{-4n} ~\biggl\{
\tilde\theta^{n-3}( -\tilde\xi^2 \tilde\theta' )^{2}  \cdot \biggl[
\frac{(n+1)^3}{3\cdot  5^3}\biggr] 
\biggl[ \frac{3^2\cdot 5}{5-n} \biggl( \frac{\tilde\theta^'}{\tilde\xi} \biggr)^2 \biggr]^{3}
\bigg( - \frac{3\tilde\theta^'}{\tilde\xi} \biggr)^{-2}
\biggr\}^{n+1}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\tilde\theta^{(n+1)(n-3)}
\tilde\mathfrak{f}_A^{-4n} ~\biggl[ \frac{3(n+1)}{(5-n)} ( -\tilde\theta' )^{2} \biggr]^{3(n+1)}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\tilde\theta^{(n+1)(n-3)}
\biggl[ \frac{3(n+1) }{(5-n)} ~( \tilde\theta^' )^2  + \tilde\theta^{n+1} \biggr]^{-4n}
~\biggl[ \frac{3(n+1)}{(5-n)} ( \tilde\theta' )^{2} \biggr]^{3(n+1)} \, .
</math>
  </td>
</tr>
</table>
</div>
(Not a particularly simple or transparent expression!)
 
=====Summary=====
Defining,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~a_\mathrm{ad}</math>
  </td>
  <td align="center">
<math>~\equiv</math>
  </td>
  <td align="left">
<math>~\frac{3(n+1) }{(5-n)} ~(\tilde\theta^' )^2 \, ,</math> &nbsp;&nbsp;&nbsp; and,
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~b_\mathrm{ad}</math>
  </td>
  <td align="center">
<math>~\equiv</math>
  </td>
  <td align="left">
<math>~\tilde\theta^{n+1} \, ,</math>
  </td>
</tr>
</table>
</div>
the expressions for the dimensionless equilibrium radius and the dimensionless external pressure may be written as, respectively,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\chi_\mathrm{ad}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\biggl[ 1 + \frac{b_\mathrm{ad}}{a_\mathrm{ad}} \biggr]^{n/(n-3)} \, ,
</math> &nbsp;&nbsp;&nbsp; and,
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\Pi_\mathrm{ad} </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
b_\mathrm{ad} \biggl[ \frac{a_\mathrm{ad}^{3(n+1)} }{( a_\mathrm{ad} + b_\mathrm{ad} )^{4n} } \biggr]^{1/(n-3)}
=
\frac{b_\mathrm{ad}}{a_\mathrm{ad}} \biggl[ 1 + \frac{b_\mathrm{ad}}{a_\mathrm{ad}} \biggr]^{-4n/(n-3)}
\, .
</math>
  </td>
</tr>
</table>
</div>
 
Using these expressions, it is easy to demonstrate that the virial equilibrium relation is satisfied, namely,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\Pi_\mathrm{ad} </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\chi_\mathrm{ad}^{-3(n+1)/n} - \chi_\mathrm{ad}^{-4} \, .</math>
  </td>
</tr>
</table>
</div>
 
{{LSU_WorkInProgress}}
 
====P-V Diagram for Unity Form Factors====
 
Writing the coefficient, <math>B</math>, in terms of the average sound speed and setting the radial scale factor equal to the equilibrium radius of an isolated adiabatic sphere, that is, setting,
<div align="center">
<math>
R_0 = \frac{GM}{5\bar{c_s}^2} \, ,
</math>
</div>
the equation governing the radii of ''adiabatic'' equilibrium states becomes,
<div align="center">
<math>
\chi^4 - \frac{1}{\Pi_a} \chi^{(4-3\gamma_g)} + \frac{1}{\Pi_a} = 0 \, ,
</math>
</div>
where,
<div align="center">
<math>
\Pi_a \equiv \frac{4\pi P_e G^3 M^2}{3\cdot 5^3 \bar{c_s}^8} \, .
</math>
</div>
As in the isothermal case, for a given choice of configuration mass and sound speed, this parameter, <math>\Pi_a</math>, can be viewed as a dimensionless external pressure.  Alternatively, for a given choice of <math>P_e</math> and <math>\bar{c_s}</math>, <math>\Pi_a^{1/2}</math> can represent a dimensionless mass; or, for a given choice of <math>M</math> and <math>P_e</math>, <math>\Pi_a^{-1/8}</math> can represent a dimensionless sound speed.  Here we will view it as a dimensionless external pressure. 
 
Unlike the isothermal case, for an arbitrary value of the adiabatic exponent, <math>\gamma_g</math>, it isn't possible to invert this equation to obtain an analytic expression for <math>\chi</math> as a function of <math>\Pi_a</math>.  But we can straightforwardly solve for <math>\Pi_a</math> as a function of <math>\chi</math>.  The solution is,
<div align="center">
<math>
\Pi_a = \frac{\chi^{(4- 3\gamma_g)} - 1}{\chi^4} \, .
</math>
</div>
For physically relevant solutions, both <math>\chi</math> and <math>\Pi_a</math> must be nonnegative.  Hence, as is illustrated by the curves in Figure 4, the physically allowable range of equilibrium radii is,
<div align="center">
<math>
1 \le \chi \le \infty \, ~~~~~\mathrm{for}~ \gamma_g < 4/3 \, ;
</math>
 
<math>
0 < \chi \le 1 \, ~~~~~~\mathrm{for}~ \gamma_g > 4/3 \, .
</math>
</div>
 
<div align="center">
<table border="2" cellpadding="8">
<tr>
  <td align="center" colspan="2">
'''Figure 4:''' <font color="darkblue">Equilibrium Adiabatic P-V Diagram </font>
  </td>
</tr>
<tr>
  <td valign="top" width=450 rowspan="1">
The curves trace out the function,
<div align="center">
<math>
\Pi_a = (\chi^{4-3\gamma_g} - 1)/\chi^4 \, ,
</math>
</div>
for six different values of <math>\gamma_g</math> (<math>2, ~5/3, ~7/5, ~6/5, ~1, ~2/3</math>, as labeled)  and show the dimensionless external pressure, <math>\Pi_a</math>, that is required to construct a nonrotating, self-gravitating, uniform density, adiabatic sphere with an equilibrium radius <math>\chi</math>.  The mathematical solution becomes unphysical wherever the pressure becomes negative.
 
The solid red curve, drawn for the case <math>\gamma_g = 1</math>, is identical to the solid black (isothermal) curve displayed above in Figure 1.
</td>
  <td align="center" bgcolor="white">
[[File:AdabaticBoundedSpheres_Virial.jpg|450px|center|Equilibrium Adiabatic P-R Diagram]]
  </td>
</tr>
</table>
</div>
 
Each of the <math>\Pi_a(\chi)</math> curves drawn in Figure 4 exhibits an extremum.  In each case this extremum occurs at a configuration radius, <math>\chi_\mathrm{extreme}</math>, given by,
<div align="center">
<math>
\frac{\partial\Pi_a}{\partial\chi} = 0 \, ,
</math>
</div>
that is, where,
<div align="center">
<math>
4 - 3\gamma_g \chi^{4-3\gamma_g} = 0 ~~~~\Rightarrow ~~~~~ \chi_\mathrm{extreme} = \biggl[ \frac{4}{3\gamma_g} \biggr]^{1/(4-3\gamma_g)} \, .
</math>
</div>
For each value of <math>\gamma_g</math>, the corresponding dimensionless pressure is,
<div align="center">
<math>
\Pi_a \biggr|_\mathrm{extreme} = \biggl(\frac{4}{3\gamma} - 1 \biggr) \biggl[ \frac{3\gamma_g}{4} \biggr]^{4/(4-3\gamma_g)} \, .
</math>
</div>
 
Note, first, that for <math>\gamma_g > 4/3</math>, an equilibrium configuration with a positive radius can be constructed for all physically realistic &#8212; that is, for all positive &#8212; values of <math>\Pi_a</math>.  Also, consistent with the behavior of the curves shown in Figure 4, the extremum arises in the regime of physically relevant &#8212; ''i.e.,'' positive &#8212; pressures only for values of <math>\gamma_g < 4/3</math>; and in each case it represents a ''maximum'' limiting pressure.
 
====Maximum Mass====
 
=====<math>n=5</math> Polytropic=====
When <math>\gamma_a = 6/5</math> &#8212; which corresponds to an <math>n=5</math> polytropic configuration &#8212; we obtain,
<div align="center">
<math>
\Pi_\mathrm{max} = \Pi_a\biggr|_\mathrm{extreme}^{(\gamma_g = 6/5)}
= \biggl( \frac{3^{18}}{2^{10}\cdot 5^{10}} \biggr) \, ,
</math>
</div>
which corresponds to a maximum mass for pressure-bounded <math>n=5</math> polytropic configurations of,
<div align="center">
<math>M_\mathrm{max} = \Pi_\mathrm{max}^{1/2}  \biggl(\frac{3\cdot 5^3}{2^2\pi} \biggr)^{1/2} \biggl( \frac{\bar{c_s}^8}{G^3 P_e} \biggr)^{1/2}
= \biggl(\frac{3^{19}}{2^{12}\cdot 5^{7}\pi} \biggr)^{1/2} \biggl( \frac{\bar{c_s}^8}{G^3 P_e} \biggr)^{1/2} \, .</math>
</div>
This result can be compared to [[User:Tohline/SSC/Structure/LimitingMasses#Bounded_Isothermal_Sphere_.26_Bonnor-Ebert_Mass|other determinations of the Bonnor-Ebert mass limit]].
 
====More Precise Form Factors====
Here we attempt to determine proper expressions for several form factors such that the equilibrium configurations determined from virial analysis will precisely match the [[User:Tohline/SSC/Structure/PolytropesEmbedded#Embedded_Polytropic_Spheres|pressure-truncated polytropic configurations]] that have been determined from detailed force-balanced models that have been derived and published separately by [http://adsabs.harvard.edu/abs/1970MNRAS.151...81H Horedt (1970)], by  [http://adsabs.harvard.edu/abs/1981MNRAS.195..967W Whitworth (1981)] and by [http://adsabs.harvard.edu/abs/1983ApJ...268..165S Stahler (1983)].  It seems simplest to begin with the [[User:Tohline/SSC/BipolytropeGeneralization_Version2#Generalized_Free-Energy_Expression|free-energy expressions that we have already generalized in the context of bipolytropic configurations]], properly modified to embed the "core" in an external medium of pressure, <math>~P_e</math>, rather then inside an envelope that has a different polytropic index.  Specifically,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\mathfrak{G}^* \equiv \frac{\mathfrak{G}}{E_\mathrm{norm}}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\biggl( \frac{W_\mathrm{grav}}{E_\mathrm{norm}} \biggr)_\mathrm{core}
+ \biggl( \frac{\mathfrak{S}_A}{E_\mathrm{norm}} \biggr)_\mathrm{core}
+ \biggl( \frac{P_e V}{E_\mathrm{norm}} \biggr)
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
-3\mathcal{A} \chi^{-1} - \frac{\mathcal{B}_\mathrm{core}}{(1-\gamma_c)} \chi^{3-3\gamma_c}  + \mathcal{D} \chi^3 \, ,
</math>
  </td>
</tr>
</table>
</div>
where,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\mathcal{A}</math>
  </td>
  <td align="center">
<math>~\equiv</math>
  </td>
  <td align="left">
<math>
\biggl( \frac{\nu}{q^3} \biggr) \int_0^{q} \biggl[\frac{M_r(x)}{M_\mathrm{tot}} \biggr]_\mathrm{core}  \biggl[ \frac{\rho(x)}{\bar\rho} \biggr]_\mathrm{core}  x dx  \, ,
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\mathcal{B}_\mathrm{core}</math>
  </td>
  <td align="center">
<math>~\equiv</math>
  </td>
  <td align="left">
<math>
\frac{4\pi}{3} \biggl[ \frac{P_{ic} \chi^{3\gamma_c}}{P_\mathrm{norm}} \biggr]_\mathrm{eq} \int_0^q  3\biggl[\frac{1 - p_c(x)}{1-p_c(q)} \biggr]  x^2 dx
=
\frac{4\pi}{3} \biggl[ \frac{P_e \chi^{3\gamma_c}}{P_\mathrm{norm}} \biggr]_\mathrm{eq} \biggl[ q^3 s_\mathrm{core} \biggr]
\, ,
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\mathcal{D}</math>
  </td>
  <td align="center">
<math>~\equiv</math>
  </td>
  <td align="left">
<math>
\chi^{-3} \biggl[ \frac{P_e V}{P_\mathrm{norm} R_\mathrm{norm}^3} \biggr] = \biggl(\frac{P_e}{P_\mathrm{norm}} \biggr) \int_0^q  4\pi  x^2 dx
= \frac{4\pi q^3}{3} \biggl(\frac{P_e}{P_\mathrm{norm}} \biggr) \, .
</math>
  </td>
</tr>
</table>
</div>
 
Virial equilibrium occurs where <math>~\partial\mathfrak{G}/\partial \chi = 0</math>, that is, when,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\mathcal{A} \chi_\mathrm{eq}^{-1}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\mathcal{B} \chi_\mathrm{eq}^{3-3\gamma_c} - \mathcal{D} \chi_\mathrm{eq}^{3} \, .</math>
  </td>
</tr>
</table>
</div>
 
=====n = 5 Polytropic=====
 
From our [[User:Tohline/SSC/Structure/BiPolytropes/FreeEnergy5_1#Free_Energy_of_BiPolytrope_with|analysis of the free energy of <math>~(n_c, n_e) = (5, 0)</math> bipolytropes]], we deduce that the coefficient, <math>~\mathcal{A}</math>, that quantifies the [[User:Tohline/SSC/Structure/BiPolytropes/FreeEnergy5_1#The_Core_2|gravitational potential energy of a pressure-truncated <math>~n = 5</math> polytrope]] is,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\mathcal{A} = - \frac{\chi}{3} \biggl( \frac{W_\mathrm{grav}}{E_\mathrm{norm}} \biggr)_\mathrm{core} </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
<td align="left">
<math>
\chi_\mathrm{eq} \biggl( \frac{3^6}{2^5\pi} \biggr)^{1/2} 
\biggl[
a_\xi^{1/2} q(a_\xi^2 q^4 - \frac{8}{3}a_\xi q^2 - 1) (a_\xi q^2 +1)^{-3} + \tan^{-1}(a_\xi^{1/2} q)
\biggr] \, ;
</math>
  </td>
</tr>
</table>
</div>
the coefficient, <math>~\mathcal{B}_\mathrm{core}</math>, that quantifies the [[User:Tohline/SSC/Structure/BiPolytropes/FreeEnergy5_1#The_Core_3|thermal energy content of a pressure-truncated <math>~n = 5</math> polytrope]] is,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\mathcal{B} = (\gamma_c-1) \chi^{3\gamma_c-3}\biggl( \frac{\mathfrak{S}_A}{E_\mathrm{norm}} \biggr)_\mathrm{core}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
\chi_\mathrm{eq}^{3/5}
\biggl( \frac{3^6}{2^5\pi} \biggr)^{1/2} \biggl[
\tan^{-1}[a_\xi^{1/2}q] - a_\xi^{1/2}q ~\frac{(1 - a_\xi q^2)}{(1 + a_\xi q^2)^2} \biggr] \, ;
</math>
  </td>
</tr>
</table>
</div>
and the coefficient, <math>~\mathcal{D}</math> &#8212; which can be obtained by setting <math>~P_{ic} \rightarrow P_e</math> in expressions drawn from out analysis of the [[User:Tohline/SSC/Structure/BiPolytropes/FreeEnergy5_1#The_Core_3|thermal energy content of an <math>~(5, 0)</math>bipolytrope]] &#8212; is,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>\mathcal{D} = \biggl(\frac{2q^3}{3 \chi_\mathrm{eq}^3} \biggr) \biggl[ \frac{2\pi P_{ic} \chi_\mathrm{eq}^3}{P_\mathrm{norm}} \biggr] </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
\chi_\mathrm{eq}^{-3} \biggl( \frac{2\cdot 3^4}{\pi} \biggr)^{1/2} \biggl(1 + a_\xi q^2 \biggr)^{-3} a_\xi^{3/2}q^3 \, .
</math>
  </td>
</tr>
</table>
</div>
Hence, virial equilibrium occurs when,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\mathcal{A} \chi_\mathrm{eq}^{-1}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\mathcal{B} \chi_\mathrm{eq}^{-3/5} - \mathcal{D} \chi_\mathrm{eq}^{3} \, ,</math>
  </td>
</tr>
</table>
</div>
that is, when,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~
\biggl( \frac{3^6}{2^5\pi} \biggr)^{1/2} 
\biggl[ a_\xi^{1/2} q(a_\xi^2 q^4 - \frac{8}{3}a_\xi q^2 - 1) (a_\xi q^2 +1)^{-3} + \tan^{-1}(a_\xi^{1/2} q)\biggr]
</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\biggl( \frac{3^6}{2^5\pi} \biggr)^{1/2} \biggl[
\tan^{-1}[a_\xi^{1/2}q] - a_\xi^{1/2}q ~\frac{(1 - a_\xi q^2)}{(1 + a_\xi q^2)^2} \biggr]
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
&nbsp;
  </td>
  <td align="left">
<math>~
-
\biggl( \frac{2\cdot 3^4}{\pi} \biggr)^{1/2} \biggl(1 + a_\xi q^2 \biggr)^{-3} a_\xi^{3/2}q^3 \, .
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\Rightarrow~~~~
\biggl[ a_\xi^{1/2} q(a_\xi^2 q^4 - \frac{8}{3}a_\xi q^2 - 1) (a_\xi q^2 +1)^{-3} + \tan^{-1}(a_\xi^{1/2} q)\biggr]
</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
\biggl[ \tan^{-1}[a_\xi^{1/2}q] - a_\xi^{1/2}q ~\frac{(1 - a_\xi q^2)}{(1 + a_\xi q^2)^2} \biggr]
-
\biggl( \frac{2^3}{3} \biggr) \biggl(1 + a_\xi q^2 \biggr)^{-3} a_\xi^{3/2}q^3</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\Rightarrow~~~~
a_\xi^{1/2} q(a_\xi^2 q^4 - \frac{8}{3}a_\xi q^2 - 1)
</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
- a_\xi^{1/2}q ~(1 - a_\xi q^2)(1 + a_\xi q^2)
-
\biggl( \frac{2^3}{3} \biggr) a_\xi^{3/2}q^3</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\Rightarrow~~~~
(a_\xi^2 q^4 - \frac{8}{3}a_\xi q^2 - 1)
</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
- (1 - a_\xi^2 q^4)  - \biggl( \frac{2^3}{3} \biggr) a_\xi q^2
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\Rightarrow~~~~
0
</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~
0 \, .
</math>
  </td>
</tr>
</table>
</div>
So this will always be true!
 
 
The [[User:Tohline/SSC/Structure/PolytropesEmbedded#Extension_to_Bounded_Sphere_2|detailed force-balanced analysis]] of <math>~n=5</math> polytropes shows that the pair of equations defining the equilibrium (truncated) radius for a specified external pressure are,
<div align="center">
<math>
R_\mathrm{eq} = \biggl[ \frac{\pi M^4 G^5}{2^3 \cdot 3^7 K^5} \biggr]^{1/2} \frac{(3+\xi_e^2)^3}{\xi_e^5} \, ,
</math>
 
<math>P_e= \biggr( \frac{2^3\cdot 3^{15} K^{10}}{\pi^3 M^{6} G^9} \biggr) \frac{\xi_e^{18}}{(3 + \xi_e^2)^{12}} </math> .
</div>
Applying our chosen normalizations, this pair of defining equations becomes,
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\chi_\mathrm{eq} = \frac{R_\mathrm{eq}}{R_\mathrm{norm}} </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\biggl[ \frac{\pi M^4 G^5}{2^3 \cdot 3^7 K^5} \biggr]^{1/2} \frac{(3+\xi_e^2)^3}{\xi_e^5}
\cdot \biggl[\frac{K^5}{G^5 M_\mathrm{tot}^4} \biggr]^{1/2}
= \biggl( \frac{\pi}{2^3 \cdot 3} \biggr)^{1/2} \xi_e^{-5}  \biggl( 1+ \frac{1}{3}\xi_e^2 \biggr)^3 \, ,
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\frac{P_e}{P_\mathrm{norm}} </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\biggr( \frac{2^3\cdot 3^{15} K^{10}}{\pi^3 M^{6} G^9} \biggr) \frac{\xi_e^{18}}{(3 + \xi_e^2)^{12}}
\cdot \biggl[\frac{G^9 M_\mathrm{tot}^6}{K^{10}} \biggr]
= \biggr( \frac{2^3\cdot 3^{3} }{\pi^3} \biggr) \xi_e^{18} \biggl(1 + \frac{1}{3}\xi_e^2 \biggr)^{-12} \, .
</math>
  </td>
</tr>
</table>
</div>
 
==Relationship to Detailed Force Balance Solution==
 
Let's plug these form-factors into our expressions for the dimensionless equilibrium radius, <math>~\chi_\mathrm{ad}</math>, and dimensionless surface pressure, <math>~\Pi_\mathrm{ad}</math>, that have been derived from the identification of extrema in the free-energy function and see how they compare to the dimensionless radius, <math>~r_a \equiv R_\mathrm{eq}/R_\mathrm{Hoerdt}</math>, and dimensionless pressure, <math>~p_a \equiv P_e/P_\mathrm{Hoerdt}</math>, given by [http://adsabs.harvard.edu/abs/1970MNRAS.151...81H Horedt's (1970)] detailed force-balance models.  Note that expressions for <math>~r_a</math> and <math>~p_a</math> are given in our [[User:Tohline/SSC/Structure/PolytropesEmbedded#Horedt.27s_Presentation|accompanying discussion of embedded polytropic spheres]] and that the conversion from Hoerdt's scaling parameters to our normalization parameters, <math>~R_\mathrm{Hoerdt}/R_\mathrm{norm}</math> and <math>~P_\mathrm{Hoerdt}/P_\mathrm{norm}</math>, can be found in our [[User:Tohline/SphericallySymmetricConfigurations/Virial#Normalizations|introductory discussion of the virial equilibrium of spherical configurations]].
 
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\chi_\mathrm{ad} \equiv \frac{R_\mathrm{eq}}{R_\mathrm{ad}}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\frac{R_\mathrm{eq}}{R_\mathrm{Hoerdt}} \biggl( \frac{R_\mathrm{Hoerdt}}{R_\mathrm{norm}} \biggr)
\biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~r_a \biggl[ \biggl(\frac{\gamma - 1}{\gamma}\biggr) (4\pi)^{\gamma-1}\biggr]^{1/(4-3\gamma)}
\biggl[ 5 \biggl( \frac{4\pi}{3} \biggr)^{1-\gamma_g} \frac{\mathfrak{f}_A}{\mathfrak{f}_W \mathfrak{f}_M^{\gamma_g-2}}
\biggr]^{1/(4-3\gamma_g)} </math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~r_a \biggl[ 5 \cdot 3^{\gamma-1} \biggl(\frac{\gamma - 1}{\gamma}\biggr)
\frac{\mathfrak{f}_A \mathfrak{f}_M^{2-\gamma_g}}{\mathfrak{f}_W }
\biggr]^{1/(4-3\gamma_g)} </math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
r_a \biggl[ \frac{5 \cdot 3^{1/n} }{n+1} \cdot \frac{\mathfrak{f}_A \mathfrak{f}_M^{(n-1)/n}}{\mathfrak{f}_W } \biggr]^{n/(n-3)}
= r_a \biggl[ 3 \mathfrak{f}_M^{n-1} \biggl( \frac{5 }{n+1} \cdot \frac{\mathfrak{f}_A }{\mathfrak{f}_W }\biggr)^n \biggr]^{1/(n-3)} 
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\Pi_\mathrm{ad} \equiv \frac{P_\mathrm{e}}{P_\mathrm{ad}}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\frac{P_\mathrm{e}}{P_\mathrm{Hoerdt}} \biggl( \frac{P_\mathrm{Hoerdt}}{P_\mathrm{norm}} \biggr)
\biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr)</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~p_a \biggl[ \biggl( \frac{\gamma}{\gamma-1}\biggr)^{3\gamma} (4\pi)^{-\gamma} \biggr]^{1/(4-3\gamma)}
\biggl[ \mathfrak{f}_A^{-4} \biggl( \frac{4\pi}{3\cdot  5^3} \cdot \frac{\mathfrak{f}_W^3}{\mathfrak{f}_M^2} \biggr)^{\gamma_g}
\biggr]^{1/(4-3\gamma_g)} </math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~p_a \mathfrak{f}_A^{-4/(4-3\gamma)} \biggl[ \biggl( \frac{\gamma}{\gamma-1}\biggr)^{3} 
\biggl( \frac{1}{3\cdot  5^3} \cdot \frac{\mathfrak{f}_W^3}{\mathfrak{f}_M^2} \biggr)\biggr]^{\gamma/(4-3\gamma)}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
~p_a \mathfrak{f}_A^{-4n/(n-3)} \biggl[ \frac{(n+1)^3}{3\cdot  5^3} \cdot \frac{\mathfrak{f}_W^3}{\mathfrak{f}_M^2} \biggr]^{(n+1)/(n-3)}
</math>
  </td>
</tr>
</table>
</div>
 
Now we insert the form-factor expressions [[User:Tohline/SSC/Virial/Polytropes#Summary|from above]], to obtain,
 
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>~\chi_\mathrm{ad} </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
r_a \biggl[ 3 \biggl( \frac{5 }{n+1} \biggr)^n \biggr]^{1/(n-3)} 
\biggl[ \frac{\mathfrak{f}_A^n \mathfrak{f}_M^{n-1} }{\mathfrak{f}_W^n } \biggr]^{1/(n-3)}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
r_a \biggl[ 3 \biggl( \frac{5 }{n+1} \biggr)^n \biggr]^{1/(n-3)} 
\biggl\{
\biggl[ \frac{3(n+1) }{(5-n)} ~( \Theta^' )^2 \biggr]^n
\biggl[ \frac{3^2\cdot 5}{5-n} \biggl( \frac{\Theta^'}{\xi} \biggr)^2 \biggr]^{-n}
\biggl[ - \frac{3\Theta^'}{\xi} \biggr]^{n-1}
\biggr\}^{1/(n-3)}_{\xi_1}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
r_a \biggl\{ 3^n \biggl( \frac{5 }{n+1} \biggr)^n \biggl[ \frac{3(n+1) }{(5-n)} \biggr]^n \biggl[ \frac{5-n}{3^2\cdot 5}  \biggr]^{n}
\biggr\}^{1/(n-3)} 
\biggl\{ \xi^{2n}
\biggl[ - \frac{\Theta^'}{\xi} \biggr]^{n-1}
\biggr\}^{1/(n-3)}_{\xi_1}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
r_a \biggl[ \xi^{n+1} ( - \Theta^' )^{n-1} \biggr]^{1/(n-3)}_{\xi_1}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>~\Pi_\mathrm{ad} </math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
~p_a \mathfrak{f}_A^{-4n/(n-3)} \biggl[ \frac{(n+1)^3}{3\cdot  5^3} \cdot \frac{\mathfrak{f}_W^3}{\mathfrak{f}_M^2} \biggr]^{(n+1)/(n-3)}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~p_a \biggl[ \frac{3(n+1) }{(5-n)} ~( \Theta^' )^2 \biggr]_{\tilde\xi}^{-4n/(n-3)}
\biggl\{
\frac{(n+1)^3}{3\cdot  5^3} \cdot
\biggl[\frac{3^2\cdot 5}{5-n} \biggl( \frac{\Theta^'}{\xi} \biggr)^2\biggr]^3
\biggl[  - \frac{3\Theta^'}{\xi} \biggr]^{-2}
\biggr\}^{(n+1)/(n-3)}_{\xi_1}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
~p_a \biggl\{ \biggl[ \frac{5-n}{3(n+1)} \biggr]^{4n} \biggl[ \frac{(n+1)^3 \cdot 3^6 \cdot 5^3}{3^3 \cdot 5^3 (5-n)^3} \biggr]^{(n+1)} \biggr\}^{1/(n-3)}
\biggl[ ( \Theta^' )^{-8n} \biggl( \frac{\Theta^'}{\xi} \biggr)^{4(n+1)}
\biggr]^{1/(n-3)}_{\xi_1}
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
~p_a \biggl[ \frac{5-n}{3(n+1)} \biggr] \biggl[\xi^{n+1} ( \Theta^' )^{n-1} \biggr]^{-4/(n-3)}_{\xi_1}
</math>
  </td>
</tr>
</table>
</div>
 
Notice that the bracketed term that is to be evaluated at <math>~\xi_1</math> is identical in both expressions.  After [[User:Tohline/SSC/Virial/Polytropes#Renormalization|renormalization, as drived above]], the statement of virial equilibrium for embedded polytropes is,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\chi_\mathrm{ad}^4</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\frac{1}{\Pi_\mathrm{ad}} \biggl[ \chi_\mathrm{ad}^{4-3\gamma_g} - 1 \biggr] \, ,</math>
  </td>
</tr>
</table>
</div>
or, setting <math>~\gamma_g = (n+1)/n</math>,
<div align="center">
<table border="0" cellpadding="5" align="center">
<tr>
  <td align="right">
<math>~\Pi_\mathrm{ad} \chi_\mathrm{ad}^4</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~\chi_\mathrm{ad}^{(n-3)/n} - 1  \, .</math>
  </td>
</tr>
</table>
</div>
This relation can now be written in terms of [http://adsabs.harvard.edu/abs/1970MNRAS.151...81H Horedt's (1970)] dimensionless radius and pressure.
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>
~p_a \biggl[ \frac{5-n}{3(n+1)} \biggr] \biggl[\xi^{n+1} ( \Theta^' )^{n-1} \biggr]^{-4/(n-3)}_{\xi_1}
\cdot r_a^4 \biggl[ \xi^{n+1} ( - \Theta^' )^{n-1} \biggr]^{4/(n-3)}_{\xi_1}
</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~ r_a^{(n-3)/n} \biggl[ \xi^{n+1} ( - \Theta^' )^{n-1} \biggr]^{1/n}_{\xi_1}  - 1</math>
  </td>
</tr>
</table>
</div>
 
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>
\Rightarrow ~~~~ p_a r_a^4 \biggl[ \frac{5-n}{3(n+1)} \biggr] 
</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~ r_a^{(n-3)/n} \biggl[ \xi^{n+1} ( - \Theta^' )^{n-1} \biggr]^{1/n}_{\xi_1}  - 1 \, ,</math>
  </td>
</tr>
</table>
</div>
where, from our separate [[User:Tohline/SSC/Structure/PolytropesEmbedded#Horedt.27s_Presentation|summary of Hoerdt's presentation]],
<div align="center">
<table border="0" cellpadding="3">
 
<tr>
  <td align="right">
<math>
~r_a
</math>
  </td>
  <td align="center">
<math>~=~</math>
  </td>
  <td align="left">
<math>
\tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)}
= \biggl[ \tilde\xi^{n+1} (-\tilde\theta^')^{n-1} \biggr]^{-1/(n-3)}\, ,
</math>
  </td>
</tr>
 
<tr>
  <td align="right">
<math>
~p_a
</math>
  </td>
  <td align="center">
<math>~=~</math>
  </td>
  <td align="left">
<math>
\tilde\theta_n^{n+1}( -\tilde\xi^2 \tilde\theta' )^{2(n+1)/(n-3)} \, .
</math>
  </td>
</tr>
</table>
</div>
Hence, the virial relation becomes,
 
<div align="center">
<table border="0" cellpadding="5" align="center">
 
<tr>
  <td align="right">
<math>
~1
</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~ \biggl\{ \frac{ [ \xi^{n+1} ( - \Theta^' )^{n-1} ]_{\xi_1} }{ [ \tilde\xi^{n+1} (-\tilde\theta^')^{n-1} ] }
\biggr\}^{1/n}
- \biggl[ \frac{5-n}{3(n+1)} \biggr] \tilde\theta_n^{n+1} \biggl\{ \frac{( -\tilde\xi^2 \tilde\theta' )^{2(n+1)/(n-3)}}{
[ \tilde\xi^{n+1} (-\tilde\theta^')^{n-1} ]^{4/(n-3)} } \biggr\}  </math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~ \biggl[ \frac{ \xi_1^{n+1} ( - \Theta^' )^{n-1}_{\xi_1} }{ \tilde\xi^{n+1} (-\tilde\theta^')^{n-1}  }
\biggr]^{1/n}
- \biggl[ \frac{5-n}{3(n+1)} \biggr] \tilde\theta_n^{n+1} \biggl\{ \frac{ \tilde\xi^{4n+4} ( -\tilde\theta' )^{2n+2}}{
\tilde\xi^{4n+4} (-\tilde\theta^')^{4n-4}  } \biggr\}^{1/(n-3)}  </math>
  </td>
</tr>
 
<tr>
  <td align="right">
&nbsp;
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>~ \biggl[ \frac{ \xi_1^{n+1} ( - \Theta^' )^{n-1}_{\xi_1} }{ \tilde\xi^{n+1} (-\tilde\theta^')^{n-1}  }
\biggr]^{1/n}
- \biggl[ \frac{5-n}{3(n+1)} \biggr] \frac{ \tilde\theta_n^{n+1} }{ ( -\tilde\theta' )^{2} } \, .</math>
  </td>
</tr>
</table>
</div>
This needs to be checked, perhaps with specific applications to the cases <math>~n=1</math> and <math>~n=5</math>.


{{LSU_HBook_footer}}
{{LSU_HBook_footer}}

Latest revision as of 19:18, 21 January 2015


Virial Equilibrium of Adiabatic Spheres

Highlights of the rather detailed discussion presented below have been summarized in an accompanying chapter of this H_Book.

Whitworth's (1981) Isothermal Free-Energy Surface
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Review

Adopted Normalizations

In an introductory discussion of the virial equilibrium structure of spherically symmetric configurations, we adopted the following physical parameter normalizations for adiabatic systems.

Adopted Normalizations for Adiabatic Systems

In Terms of <math>~\gamma_g</math>

In Terms of <math>~n</math>

<math>~R_\mathrm{norm}</math>

<math>~\equiv</math>

<math>~\biggl[ \biggl( \frac{G}{K} \biggr) M_\mathrm{tot}^{2-\gamma_g} \biggr]^{1/(4-3\gamma_g)} </math>

<math>~P_\mathrm{norm}</math>

<math>~\equiv</math>

<math>~\biggl[ \frac{K^4}{G^{3\gamma_g} M_\mathrm{tot}^{2\gamma_g}} \biggr]^{1/(4-3\gamma_g)} </math>


<math>~E_\mathrm{norm}</math>

<math>~\equiv</math>

<math>~ P_\mathrm{norm} R_\mathrm{norm}^3 = \biggl[ KG^{3(1-\gamma_g)}M_\mathrm{tot}^{6-5\gamma_g} \biggr]^{1/(4-3\gamma_g)} </math>

<math>~\rho_\mathrm{norm}</math>

<math>~\equiv</math>

<math>~\frac{3M_\mathrm{tot}}{4\pi R_\mathrm{norm}^3} = \frac{3}{4\pi} \biggl[ \frac{K^3}{G^3 M_\mathrm{tot}^2} \biggr]^{1/(4-3\gamma_g )} </math>

<math>~c^2_\mathrm{norm}</math>

<math>~\equiv</math>

<math>~\frac{P_\mathrm{norm}}{\rho_\mathrm{norm}} = \frac{4\pi}{3} \biggl[ \frac{K}{(G^3 M_\mathrm{tot}^2)^{\gamma_g-1}} \biggr]^{1/(4-3\gamma_g )} </math>

<math>~R_\mathrm{norm}</math>

<math>~=</math>

<math>~\biggl[ \biggl( \frac{G}{K} \biggr)^n M_\mathrm{tot}^{n-1} \biggr]^{1/(n-3)} </math>

<math>~P_\mathrm{norm}</math>

<math>~=</math>

<math>~\biggl[ \frac{K^{4n}}{G^{3(n+1)} M_\mathrm{tot}^{2(n+1)}} \biggr]^{1/(n-3)} </math>


<math>~E_\mathrm{norm}</math>

<math>~=</math>

<math>~ \biggl[ K^n G^{-3}M_\mathrm{tot}^{n-5} \biggr]^{1/(n-3)} </math>

<math>~\rho_\mathrm{norm}</math>

<math>~=</math>

<math>~ \frac{3}{4\pi} \biggl[ \frac{K^3}{G^3 M_\mathrm{tot}^2} \biggr]^{n/(n-3 )} </math>

<math>~c^2_\mathrm{norm}</math>

<math>~=</math>

<math> ~\frac{4\pi}{3} \biggl[ \frac{K^n}{G^3 M_\mathrm{tot}^2} \biggr]^{1/(n-3 )} </math>

Virial Equilibrium

Also in our introductory discussion — see especially the section titled, Energy Extrema — we deduced that an adiabatic system's dimensionless equilibrium radius,

<math>~\chi_\mathrm{eq} \equiv \frac{R_\mathrm{eq}}{R_\mathrm{norm}} \, ,</math>

is given by the root(s) of the following equation:

<math> 2\mathcal{C} \chi_\mathrm{eq}^{-2} + ~3 \mathcal{B}\chi_\mathrm{eq}^{3 -3\gamma_g} -~3\mathcal{A}\chi_\mathrm{eq}^{-1} -~ 3\mathcal{D} \chi_\mathrm{eq}^3 = 0 \, , </math>

where the definitions of the various coefficients are,

<math>~\mathcal{A}</math>

<math>~\equiv</math>

<math>\frac{1}{5} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W \, ,</math>

<math>~\mathcal{B}</math>

<math>~\equiv</math>

<math> \frac{4\pi}{3} \biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr) \frac{1}{\mathfrak{f}_M} \biggr]_\mathrm{eq}^{\gamma} \cdot \mathfrak{f}_A </math>

 

<math>~=</math>

<math> \frac{4\pi}{3} \biggl[ \biggl( \frac{P_c}{P_\mathrm{norm}} \biggr)\chi^{3\gamma} \biggr]_\mathrm{eq} \cdot \mathfrak{f}_A \, , </math>

<math>~\mathcal{C}</math>

<math>~\equiv</math>

<math> \frac{3\cdot 5}{2^4 \pi} \biggl[ \frac{J^2 c_\mathrm{norm}^2}{G^2 M_\mathrm{tot}^4} \biggr] \cdot \frac{\mathfrak{f}_T}{\mathfrak{f}_M} \, , </math>

<math>~\mathcal{D}</math>

<math>~\equiv</math>

<math> \biggl( \frac{4\pi}{3} \biggr) \frac{P_e}{P_\mathrm{norm}} \, . </math>

(The dimensionless structural form factors, <math>~\mathfrak{f}_i,</math> that appear in these expressions are defined for isolated polytropes in our accompanying introductory discussion and are discussed further, below.) Once the pressure exerted by the external medium (<math>~P_e</math>), and the configuration's mass (<math>~M_\mathrm{tot}</math>), angular momentum (<math>~J</math>), and specific entropy (via <math>~K</math>) have been specified, the values of all of the coefficients are known and <math>~\chi_\mathrm{eq}</math> can be determined.


For later use, we note that after making the substitution, <math>~\gamma_g \rightarrow (n+1)/n</math>,

<math>~\biggl( \frac{\mathcal{A}}{\mathcal{B}} \biggr)^n</math>

<math>~=</math>

<math>~\biggl\{ \frac{3}{20\pi} \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W \biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr) \frac{1}{\mathfrak{f}_M} \biggr]^{-(n+1)/n} \cdot \mathfrak{f}_A^{-1} \biggr\}^n</math>

 

<math>~=</math>

<math>~5^{-n} \biggl( \frac{3}{4\pi} \biggr)^n \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^{2n} \biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr) \frac{1}{\mathfrak{f}_M} \biggr]^{-(n+1)} \cdot \biggl( \frac{\mathfrak{f}_W}{\mathfrak{f}_A} \biggr)^{n} </math>

 

<math>~=</math>

<math>~\frac{1}{5^n} \biggl( \frac{4\pi}{3} \biggr) \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)^{n-1} \cdot \frac{\mathfrak{f}_W^n}{\mathfrak{f}_A^n \mathfrak{f}_M^{n-1}} \, ; </math>

and,

<math>~\frac{\mathcal{B}^{4n}}{\mathcal{A}^{3(n+1)}}</math>

<math>~=</math>

<math>~\biggl\{ \frac{1}{5} \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W \biggr\}^{-3(n+1)} \biggl\{ \frac{4\pi}{3} \biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr) \frac{1}{\mathfrak{f}_M} \biggr]^{(n+1)/n} \cdot \mathfrak{f}_A \biggr\}^{4n}</math>

 

<math>~=</math>

<math>~ 5^{3(n+1)} \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^{-6(n+1)} \biggl( \frac{4\pi}{3} \biggr)^{4n-4(n+1)} \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr) \frac{1}{\mathfrak{f}_M} \biggr]^{4(n+1)} \cdot\frac{\mathfrak{f}_A^{4n}}{\mathfrak{f}_W^{3(n+1)}} </math>

 

<math>~=</math>

<math>~ 5^{3(n+1)} \biggl( \frac{3}{4\pi} \biggr)^{4} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2(n+1)} \cdot\frac{\mathfrak{f}_A^{4n} \mathfrak{f}_M^{2(n+1)} }{\mathfrak{f}_W^{3(n+1)}} </math>

Isolated Nonrotating Adiabatic Configuration

For a nonrotating configuration <math>~(C=J=0)</math> that is not influenced by the effects of a bounding external medium <math>~(D=P_e = 0)</math>, the statement of virial equilibrium is,

<math> 3 B\chi_\mathrm{eq}^{3 -3\gamma_g} -~3A\chi_\mathrm{eq}^{-1} = 0 \, . </math>

Hence, one equilibrium state exists for each value of <math>~\gamma_g</math> and it occurs where,

<math>~\chi_\mathrm{eq}^{4-3\gamma_g} = \biggl( \frac{R_\mathrm{eq}}{R_\mathrm{norm}} \biggr)^{4-3\gamma_g} </math>

<math>~=</math>

<math> \frac{A}{B} \, . </math>

Two Points of View

In terms of <math>~K</math> and <math>~M_\mathrm{limit} ~(= M_\mathrm{tot})</math>

In terms of <math>~P_c</math> and <math>~M_\mathrm{limit} ~(= M_\mathrm{tot})</math>

<math>~\chi_\mathrm{eq}^{4-3\gamma_g}</math>

<math>~=</math>

<math> \biggl\{ \frac{1}{5} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W \biggr\} </math>

 

 

<math> \times \biggl\{ \frac{3}{4\pi} \biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr) \frac{1}{\mathfrak{f}_M} \biggr]_\mathrm{eq}^{-{\gamma_g}} \cdot \frac{1}{\mathfrak{f}_A} \biggr\} </math>

<math>~\Rightarrow~~~R_\mathrm{eq}^{4-3\gamma_g}</math>

<math>~=</math>

<math> \frac{4\pi}{3\cdot 5} \biggl[ \frac{3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr) \frac{1}{\mathfrak{f}_M} \biggr]_\mathrm{eq}^{2-{\gamma_g}} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A} \biggl[ \frac{GM_\mathrm{tot}^{2-\gamma_g}}{K} \biggr] </math>

<math>\Rightarrow ~~\frac{KR_\mathrm{eq}^{4-3\gamma_g}}{GM_\mathrm{limit}^{2-\gamma_g}}</math>

<math>~=</math>

<math> \frac{1}{5} \biggl( \frac{4\pi}{3} \biggr)^{\gamma_g-1} \frac{\mathfrak{f}_W}{\mathfrak{f}_A \mathfrak{f}_M^{2-\gamma_g}} </math>

— — — — — —     or, inverted and setting <math>~\gamma_g = 1 + 1/n</math>     — — — — — —

<math>~ 4\pi \biggl( \frac{G}{K} \biggr)^n M_\mathrm{limit}^{n-1} R_\mathrm{eq}^{3-n} = \biggl( \frac{5 \mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} \biggr)^n \frac{3}{\mathfrak{f}_M} </math>

<math>~\chi_\mathrm{eq}^{4-3\gamma_g}</math>

<math>~=</math>

<math> \biggl\{ \frac{1}{5} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W \biggr\} </math>

 

 

<math> \times \biggl\{ \frac{3} {4\pi} \biggl[ \biggl( \frac{P_\mathrm{norm}}{P_c} \biggr)\chi^{-3\gamma} \biggr]_\mathrm{eq} \cdot \frac{1}{\mathfrak{f}_A} \biggr\} </math>

<math>~\Rightarrow~~~\chi_\mathrm{eq}^{4}</math>

<math>~=</math>

<math> \frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2 \biggl( \frac{P_\mathrm{norm}}{P_c} \biggr) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \cdot \mathfrak{f}_M^2} </math>

<math>~\Rightarrow~~~\frac{P_c R_\mathrm{eq}^{4}}{P_\mathrm{norm} R_\mathrm{norm}^4} \biggl( \frac{M_\mathrm{tot}}{M_\mathrm{limit}} \biggr)^{2}</math>

<math>~=</math>

<math> \frac{3}{20\pi} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \cdot \mathfrak{f}_M^2} </math>

<math>~\Rightarrow~~~\frac{P_c R_\mathrm{eq}^{4}}{G M_\mathrm{limit}^2} </math>

<math>~=</math>

<math> \frac{3}{20\pi} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \cdot \mathfrak{f}_M^2} </math>

According to the solution shown in the left-hand column, for fluid with a given specify entropy content, the equilibrium mass-radius relationship for adiabatic configurations is,

<math> M_\mathrm{tot}^{(\gamma_g - 2)} \propto R_\mathrm{eq}^{(3\gamma_g -4)} \, . </math>

We see that, for <math>~\gamma_g=2</math>, the equilibrium radius depends only on the specific entropy of the gas and is independent of the configuration's mass. Conversely, for <math>~\gamma_g = 4/3</math>, the mass of the configuration is independent of the radius. For <math>~\gamma_g > 2</math> or <math>~\gamma_g < 4/3</math>, configurations with larger mass (but the same specific entropy) have larger equilibrium radii. However, for <math>~\gamma_g</math> in the range, <math>~2 > \gamma_g > 4/3</math>, configurations with larger mass have smaller equilibrium radii. (Note that the related result for isothermal configurations can be obtained by setting <math>~\gamma_g = 1</math> in this adiabatic solution, because <math>~K = c_s^2</math> when <math>~\gamma_g = 1</math>.)

Role of Structural Form Factors

When employing a virial analysis to determine the radius of an equilibrium configuration, it is customary to set the structural form factors, <math>~\mathfrak{f}_M</math>, <math>~\mathfrak{f}_W</math> and <math>~\mathfrak{f}_A</math>, to unity and accept that the expression derived for <math>~R_\mathrm{eq}</math> is an estimate of the configuration's radius that is good to within a factor of order unity. As has been demonstrated in our related discussion of the equilibrium of uniform-density spheres, these form factors can be evaluated if/when the internal structural profile of an equilibrium configuration is known from a complementary detailed force-balance analysis. In the case being discussed here of isolated, spherical polytropes, solutions to the,

Lane-Emden Equation

LSU Key.png

<math>~\frac{1}{\xi^2} \frac{d}{d\xi}\biggl( \xi^2 \frac{d\Theta_H}{d\xi} \biggr) = - \Theta_H^n</math>

can provide the desired internal structural information. Here we draw on Chandrasekhar's [C67] discussion of the structure of spherical polytropes to show precisely how our structural form factors can be expressed in terms of the Lane-Emden function, <math>~\Theta_H</math>, dimensionless radial coordinate, <math>~\xi</math>, and the function derivative, <math>~\Theta^' = d\Theta_H/d\xi</math>.

Mass

We note, first, that Chandrasekhar [C67] — see his Equation (78) on p. 99 — presents the following expression for the mean-to-central density ratio:

<math>~\frac{\bar\rho}{\rho_c}</math>

<math>~=</math>

<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\xi_1} \, ,</math>

where the notation at the bottom of the closing square bracket means that everything inside the square brackets should be, "evaluated at the surface of the configuration," that is, at the radial location, <math>~\xi_1</math>, where the Lane-Emden function, <math>~\Theta_H(\xi)</math>, first goes to zero. But, as we pointed out when defining the structural form factors, the form factor associated with the configuration mass, <math>~\mathfrak{f}_M</math>, is equivalent to the mean-to-central density ratio. We conclude, therefore, that,

<math>~\mathfrak{f}_M</math>

<math>~=</math>

<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\xi_1} \, .</math>


Gravitational Potential Energy

Second, we note that Chandrasekhar's [C67] expression for the gravitational potential energy — see his Equation (90), p. 101 — is,

<math>~-W</math>

<math>~=</math>

<math>~\frac{3}{5-n} \biggl( \frac{GM^2}{R} \biggr) \, ,</math>

whereas our analogous expression is,

<math>~-W_\mathrm{grav}</math>

<math>~=</math>

<math>~\frac{3}{5} \biggl( \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}} \biggr) \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \, .</math>

We conclude, therefore, that,

<math>~\frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} </math>

<math>~=</math>

<math>~\frac{5}{5-n} </math>

<math>\Rightarrow ~~~~\mathfrak{f}_W </math>

<math>~=</math>

<math>~\frac{3^2\cdot 5}{5-n} \biggl[ \frac{\Theta^'}{\xi} \biggr]^2_{\xi_1} \, .</math>

Mass-Radius Relationship

Third, Chandrasekhar [C67] shows — see his Equation (72), p. 98 — that the general mass-radius relationship for isolated spherical polytropes is,

<math>~GM^{(n-1)/n} R^{(3-n)/n}</math>

<math>~=</math>

<math> ~\frac{(n+1)K}{(4\pi)^{1/n}} \biggl[ - \xi^{(n+1)/(n-1)} \frac{d\Theta_H}{d\xi} \biggr]^{(n-1)/n}_{\xi=\xi_1} \, , </math>

which we choose to rewrite as,

<math>~4\pi \biggl( \frac{G}{K}\biggr)^n M^{(n-1)} R^{(3-n)}</math>

<math>~=</math>

<math> ~(n+1)^n\biggl[ \xi^{(n+1)} (-\Theta^')^{(n-1)}\biggr]_{\xi=\xi_1} </math>

 

<math>~=</math>

<math> - \biggl( \frac{\xi}{\Theta^'} \biggr)_{\xi=\xi_1} \biggl[ (n+1) \xi ~(-\Theta^') \biggr]^n_{\xi=\xi_1} \, . </math>

By comparison, the expression for the equilibrium radius that has been derived, above, from an analysis of extrema in the free energy function — specifically, see the last expression in the left-hand column of the table titled "Two Points of View" — we obtain,

<math>~4\pi \biggl( \frac{G}{K}\biggr)^n M^{(n-1)} R_\mathrm{eq}^{(3-n)}</math>

<math>~=</math>

<math> ~\frac{3}{\mathfrak{f}_M} \biggl( \frac{5\mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} \biggr)^n \, . </math>

Hence, it appears as though, quite generally,

<math>~ \frac{1}{\mathfrak{f}_M} \biggl( \frac{5\mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} \biggr)^n </math>

<math>~=</math>

<math> - \biggl( \frac{\xi}{3\Theta^'} \biggr)_{\xi=\xi_1} \biggl[ (n+1) \xi ~(-\Theta^') \biggr]^n_{\xi=\xi_1} \, . </math>

Or, taking into account the expressions for <math>~\mathfrak{f}_M</math> and <math>~\mathfrak{f}_W</math> that have just been uncovered, we conclude that,

<math>~ \frac{5\mathfrak{f}_A \mathfrak{f}_M}{\mathfrak{f}_W} </math>

<math>~=</math>

<math> \biggl[ (n+1) \xi ~(-\Theta^') \biggr]_{\xi=\xi_1} </math>

<math>\Rightarrow ~~~~ \frac{\mathfrak{f}_A}{\mathfrak{f}_W} </math>

<math>~=</math>

<math> \frac{(n+1) }{3\cdot 5} ~\xi_1^2 \, . </math>

<math>\Rightarrow ~~~~ \mathfrak{f}_A </math>

<math>~=</math>

<math> \frac{(n+1) }{3\cdot 5} ~\xi_1^2 \biggl\{ \frac{3^2\cdot 5}{5-n} \biggl[ \frac{\Theta^'}{\xi} \biggr]^2_{\xi_1} \biggr\}\, . </math>

 

<math>~=</math>

<math> \frac{3(n+1) }{(5-n)} ~\biggl[ \Theta^' \biggr]^2_{\xi_1} \, . </math>

Central and Mean Pressure

It is also worth pointing out that Chandrasekhar [C67] — see his Equations (80) & (81), p. 99 — introduces a dimensionless structural form factor, <math>~W_n</math>, for the central pressure via the expression,

<math>~P_c</math>

<math>~=</math>

<math>~W_n \biggl( \frac{GM^2}{R^4} \biggr) \, ,</math>

and demonstrates that,

<math>~\frac{1}{W_n}</math>

<math>~\equiv</math>

<math>~4\pi (n+1) \biggl[ \Theta^' \biggr]^2_{\xi_1} \, .</math>

It is therefore clear that a spherical polytrope's central pressure is expressible in terms of our structural form factor, <math>~\mathfrak{f}_A</math>, as,

<math>~P_c</math>

<math>~=</math>

<math>~\frac{3}{4\pi (5-n)} \biggl( \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}^4} \biggr) \frac{1}{\mathfrak{f}_A} \, .</math>

Looking back at our original definition of the structural form factors, we note that,

<math>\mathfrak{f}_A = \biggl( \frac{\bar{P}}{P_c} \biggr)_\mathrm{eq} \, .</math>

Hence, this last equilibrium relation can be rewritten as,

<math> \frac{\bar{P} R_\mathrm{eq}^4}{GM_\mathrm{tot}^2} = \frac{3}{4\pi (5-n)} \, .</math>

Alternate Derivation of Gravitational Potential Energy

As has been discussed elsewhere, we have learned from Chandrasekhar's discussion of polytropic spheres [C67] — see his Equation (16), p. 64 — that if a spherically symmetric system is in hydrostatic balance, the total gravitational potential energy can be obtained from the following integral:

<math>~W_\mathrm{grav}</math>

<math>~=</math>

<math>~ + \frac{1}{2} \int_0^R \Phi(r) dm \, .</math>

Using "technique #3" to solve the differential equation that governs the statement of hydrostatic balance, we know that in any polytropic sphere, <math>~\Phi(r)</math> is related to the configuration's radial enthalpy profile, <math>~H(r)</math>, via the algebraic expression,

<math>~\Phi(r) + H(r)</math>

<math>~=</math>

<math>~C_B \, ,</math>

where, <math>~C_B</math>, is an integration constant. At the surface of the equilibrium configuration, <math>~H = 0</math> and <math>~\Phi = - GM_\mathrm{tot}/R_\mathrm{eq}</math>, so the integration constant is,

<math>~C_B</math>

<math>~=</math>

<math>~- \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \, ,</math>

which implies,

<math>~\Phi(r) </math>

<math>~=</math>

<math>~ - H(r) - \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \, .</math>

Now, from our general discussion of barotropic relations, we can write,

<math>~H(r)</math>

<math>~=</math>

<math>~(n+1) \frac{P(r)}{\rho(r)} \, .</math>

Hence,

<math>~-\Phi(r)</math>

<math>~=</math>

<math>~(n+1) \frac{P(r)}{\rho(r)} + \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \, ,</math>

and,

<math>~W_\mathrm{grav}</math>

<math>~=</math>

<math>~ - \frac{1}{2} \int_0^R \biggl[ (n+1) \frac{P(r)}{\rho(r)} + \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \biggr] 4\pi \rho(r) r^2 dr </math>

 

<math>~=</math>

<math>~ - 2\pi \biggl\{ (n+1) \int_0^R P(r) r^2 dr + \frac{GM_\mathrm{tot}}{R_\mathrm{eq}} \int_0^R \rho(r) r^2 dr \biggr\} </math>

 

<math>~=</math>

<math>~ - 2\pi \biggl\{ \frac{1}{3} (n+1)P_c R_\mathrm{eq}^3 \int_0^1 3\biggl[ \frac{P(x)}{P_c} \biggr] x^2 dx + \frac{GM_\mathrm{tot}}{3R_\mathrm{eq}} \biggl( \rho_c R_\mathrm{eq}^3 \biggr) \int_0^1 3 \biggl[ \frac{\rho(x)}{\rho_c} \biggr] x^2 dx \biggr\} </math>

 

<math>~=</math>

<math>~ - 2\pi \biggl\{ \frac{1}{3} (n+1)P_c R_\mathrm{eq}^3 \mathfrak{f}_A + \frac{GM_\mathrm{tot}}{3R_\mathrm{eq}} \biggl( \rho_c R_\mathrm{eq}^3 \biggr) \mathfrak{f}_M \biggr\} </math>

 

<math>~=</math>

<math>~ - \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}} \biggl\{ \frac{2\pi}{3} (n+1) \biggl[ \frac{P_c R_\mathrm{eq}^4}{GM_\mathrm{tot}^2} \biggr] \mathfrak{f}_A + \frac{1}{2} \biggl[ \frac{4\pi \rho_c R_\mathrm{eq}^3}{3M_\mathrm{tot}} \biggr] \mathfrak{f}_M \biggr\} </math>

 

<math>~=</math>

<math>~ - \frac{1}{2} \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}} \biggl\{ \frac{4\pi}{3} (n+1) \biggl[ \frac{P_c R_\mathrm{eq}^4}{GM_\mathrm{tot}^2} \biggr] \mathfrak{f}_A + 1 \biggr\} \, .</math>

We now recall two earlier expressions that show the role that our structural form factors play in the evaluation of <math>~W</math> and <math>~P_c</math>, namely,

<math>~W_\mathrm{grav}</math>

<math>~=</math>

<math>~ - \frac{3}{5} \biggl( \frac{GM_\mathrm{tot}^2}{R_\mathrm{eq}} \biggr) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>

and,

<math>~P_c</math>

<math>~=</math>

<math>~ \frac{3 }{20\pi }\biggl( \frac{G M_\mathrm{tot}^2}{R_\mathrm{eq}^4} \biggr) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \mathfrak{f}_M^2} \, .</math>

Plugging these into our newly derived expression for the gravitational potential energy gives,

<math>~- \frac{3}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>

<math>~=</math>

<math>~ - \frac{1}{2} \biggl\{ \frac{4\pi}{3} (n+1) \biggl[ \frac{3 }{20\pi }\cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_A \mathfrak{f}_M^2} \biggr] \mathfrak{f}_A + 1 \biggr\} </math>

<math>\Rightarrow ~~~~ (2\cdot 3) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>

<math>~=</math>

<math>~ (n+1) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} + 5 </math>

<math>\Rightarrow ~~~~ (5 - n) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>

<math>~=</math>

<math>~ 5 </math>

<math>\Rightarrow ~~~~ \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2}</math>

<math>~=</math>

<math>~ \frac{5}{5-n} \, . </math>

As it should, this agrees with the expression for the ratio, <math>\mathfrak{f}_W/\mathfrak{f}_M^2</math>, that was derived in our above discussion of the gravitational potential energy.

Summary

In summary, expressions for the three structural form factors associated with isolated, spherically symmetric polytropes are as follows:

Structural Form Factors for Isolated Polytropes

<math>~\mathfrak{f}_M</math>

<math>~=</math>

<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\xi_1} </math>

<math>\mathfrak{f}_W </math>

<math>~=</math>

<math>~\frac{3^2\cdot 5}{5-n} \biggl[ \frac{\Theta^'}{\xi} \biggr]^2_{\xi_1} </math>

<math>\mathfrak{f}_A </math>

<math>~=</math>

<math> \frac{3(n+1) }{(5-n)} ~\biggl[ \Theta^' \biggr]^2_{\xi_1} </math>

Nonrotating Adiabatic Configuration Embedded in an External Medium

For a nonrotating configuration <math>~(C=J=0)</math> that is embedded in, and is influenced by the pressure <math>~P_e</math> of, an external medium, the statement of virial equilibrium is,

<math> 3 B\chi_\mathrm{eq}^{3 -3\gamma_g} -~3A\chi_\mathrm{eq}^{-1} -~ 3D\chi_\mathrm{eq}^3 = 0 \, . </math>


Solution Expressed in Terms of K and M (Whitworth's 1981 Relation)

This is precisely the same condition that derives from setting equation (3) to zero in Whitworth's (1981, MNRAS, 195, 967) discussion of the Global Gravitational Stability for One-dimensional Polytropes. The overlap with Whitworth's narative is clearer after introducing the algebraic expressions for the coefficients <math>~A</math>, <math>~B</math>, and <math>~D</math>, to obtain,

<math>~4\pi \biggl( \frac{P_e}{P_\mathrm{norm}} \biggr) \chi_\mathrm{eq}^3 </math>

<math>~=</math>

<math>~3 \biggl( \frac{4\pi}{3} \biggr)^{1-\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}} \cdot \chi_\mathrm{eq}^{3 -3\gamma_g} ~-~\frac{3}{5} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2 \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \cdot \chi_\mathrm{eq}^{-1} \, ;</math>

dividing the equation through by <math>~(4\pi \chi_\mathrm{eq}^3/P_\mathrm{norm})</math>,

<math>~P_e </math>

<math>~=</math>

<math>~P_\mathrm{norm} \biggl[ \biggl( \frac{3}{4\pi} \biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}} \cdot \chi_\mathrm{eq}^{-3\gamma_g} ~- \biggl(\frac{3}{20\pi} \biggr) \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2 \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \cdot \chi_\mathrm{eq}^{-4} \biggr] </math>

 

<math>~=</math>

<math>~P_\mathrm{norm} R_\mathrm{norm}^4\biggl[ \biggl( \frac{3}{4\pi R_\mathrm{eq}^3} \biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}} \cdot R_\mathrm{norm}^{3\gamma_g-4} - \biggl(\frac{3}{20\pi R_\mathrm{eq}^4} \biggr)\biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2 \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \biggr] \, ;</math>

and inserting expressions for the parameter normalizations as defined in our accompanying introductory discussion to obtain,

<math>~P_e </math>

<math>~=</math>

<math>~GM_\mathrm{tot}^2\biggl[ \biggl( \frac{3}{4\pi R_\mathrm{eq}^3} \biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}} \cdot \frac{K M_\mathrm{tot}^{\gamma_g-2}}{G} - \biggl(\frac{3}{20\pi R_\mathrm{eq}^4} \biggr) \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^2 \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \biggr] </math>

 

<math>~=</math>

<math>~K \biggl( \frac{3M_\mathrm{limit}}{4\pi R_\mathrm{eq}^3} \biggr)^{\gamma_g} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{\gamma_g}} - \biggl(\frac{3GM_\mathrm{limit}^2}{20\pi R_\mathrm{eq}^4} \biggr) \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \, .</math>

If the structural form factors are set equal to unity, this exactly matches equation (5) of Whitworth, which reads:

Whitworth (1981, MNRAS, 195, 967)

Notice that, when <math>~P_e \rightarrow 0</math>, this expression reduces to the solution we obtained for an isolated polytrope, expressed in terms of <math>~K</math> and <math>~M_\mathrm{limit}</math> (see the left-hand column of our table titled "Two Points of View").

Solution Expressed in Terms of M and Central Pressure

Beginning again with the relevant statement of virial equilibirum, namely,

<math> A = B\chi_\mathrm{eq}^{4 -3\gamma_g} -~ D\chi_\mathrm{eq}^4 \, , </math>

but adopting the alternate expression for the coefficient, <math>~B</math>, given above, that is,

<math> B = \frac{4\pi}{3} \biggl[ \biggl( \frac{P_c}{P_\mathrm{norm}} \biggr)\chi^{3\gamma} \biggr]_\mathrm{eq} \cdot \mathfrak{f}_A \, , </math>

we can write,

<math>~\frac{1}{5} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W</math>

<math>~=</math>

<math>~ \frac{4\pi}{3} \biggl[ \biggl( \frac{P_c}{P_\mathrm{norm}} \biggr)\chi^{3\gamma} \biggr]_\mathrm{eq} \mathfrak{f}_A \cdot \chi_\mathrm{eq}^{4 -3\gamma_g} -~ \biggl( \frac{4\pi}{3} \biggr) \frac{P_e}{P_\mathrm{norm}} \chi_\mathrm{eq}^4 </math>

<math>~\Rightarrow~~~\frac{3}{20\pi} \cdot \biggl[ \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr) \frac{1}{\mathfrak{f}_M} \biggr]^2 \cdot \mathfrak{f}_W</math>

<math>~=</math>

<math>~ \biggl[ \biggl( \frac{P_c}{P_\mathrm{norm}} \biggr) \mathfrak{f}_A -~ \frac{P_e}{P_\mathrm{norm}} \biggr] \chi_\mathrm{eq}^4 </math>

 

<math>~=</math>

<math>~ \biggl[ \mathfrak{f}_A P_c -~ P_e\biggr] \frac{R_\mathrm{eq}^4}{G M_\mathrm{tot}^2} </math>

<math>\Rightarrow ~~~ \frac{3}{20\pi} \biggl( \frac{G M_\mathrm{limit}^2}{R_\mathrm{eq}^4}\biggr) \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} </math>

<math>~=</math>

<math>~ \mathfrak{f}_A P_c -~ P_e \, . </math>

Again notice that, when <math>~P_e \rightarrow 0</math>, this expression reduces to the solution we obtained for an isolated polytrope, but this time expressed in terms of <math>~P_c</math> and <math>~M_\mathrm{limit}</math> (see the right-hand column of our table titled "Two Points of View").

Contrast with Detailed Force-Balanced Solution

As has just been demonstrated, the virial theorem provides a mathematical expression that allows us to relate the equilibrium radius of a configuration to the applied external pressure, once the configuration's mass and either its specific entropy or central pressure are specified. In contrast to this, as has been discussed in detail in another chapter, Horedt (1970), Whitworth (1981) and Stahler (1983) have each derived separate analytic expressions for <math>~R_\mathrm{eq}</math> and <math>~P_e</math> — given in terms of the Lane-Emden function, <math>~\Theta</math>, and its radial derivative — without demonstrating how the equilibrium radius and external pressure directly relate to one another. That is to say, solution of the detailed force-balanced equations provides a pair of equilibrium expressions that are parametrically related to one another through the Lane-Emden function. For example — see our related discussion for more details — Horedt derives the following set of parametric equations relating the configuration's dimensionless radius, <math>~r_a</math>, to a specified dimensionless bounding pressure, <math>~p_a</math>:

<math> ~r_a \equiv \frac{R_\mathrm{eq}}{R_\mathrm{Horedt}} </math>

<math>~=~</math>

<math> \tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)} \, , </math>

<math> ~p_a \equiv \frac{P_\mathrm{e}}{P_\mathrm{Horedt}} </math>

<math>~=~</math>

<math> \tilde\theta_n^{n+1}( -\tilde\xi^2 \tilde\theta' )^{2(n+1)/(n-3)} \, , </math>

where,

<math> ~R_\mathrm{Horedt} </math>

<math>~=</math>

<math> \biggl[ \frac{4\pi}{(n+1)^n}\biggl( \frac{G}{K} \biggr)^n M_\mathrm{limit}^{n-1} \biggr]^{1/(n-3)} \, , </math>

<math> ~P_\mathrm{Horedt} </math>

<math>~=</math>

<math> K^{4n/(n-3)}\biggl[ \frac{(n+1)^3}{4\pi G^3 M_\mathrm{limit}^2} \biggr]^{(n+1)/(n-3)} \, . </math>

It is important to appreciate that, in the expressions for <math>~r_a</math> and <math>~p_a</math>, the tilde indicates that the Lane-Emden function and its derivative are to be evaluated, not at the radial coordinate, <math>~\xi_1</math>, that is traditionally associated with the "first zero" of the Lane-Emden function and therefore with the surface of the isolated polytrope, but at the radial coordinate, <math>~\tilde\xi</math>, where the internal pressure of the isolated polytrope equals <math>~P_e</math> and at which the embedded polytrope is to be truncated. The coordinate, <math>~\tilde\xi</math>, therefore identifies the surface of the embedded — or, pressure-truncated — polytrope. We also have taken the liberty of attaching the subscript "limit" to <math>~M</math> in both defining relations because it is clear that Hoerdt intended for the normalization mass to be the mass of the pressure-truncated object, not the mass of the associated isolated (and untruncated) polytrope. In anticipation of further derivations, below, we note here the ratio of Hoerdt's normalization parameters to ours, assuming <math>~\gamma = (n+1)/n</math>:

<math>~\biggl( \frac{R_\mathrm{Hoerdt}}{R_\mathrm{norm}} \biggr)^{n-3}</math>

<math>~=</math>

<math>~ \biggl[ \frac{4\pi}{(n+1)^n}\biggl( \frac{G}{K} \biggr)^n M_\mathrm{limit}^{n-1} \biggr] \biggl[ \biggl( \frac{K}{G}\biggr)^n M_\mathrm{tot}^{1-n}\biggr] </math>

 

<math>~=</math>

<math>~ \frac{4\pi}{(n+1)^n} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)^{n-1} \, , </math>

<math>~\biggl( \frac{P_\mathrm{Hoerdt}}{P_\mathrm{norm}} \biggr)^{n-3}</math>

<math>~=</math>

<math>~ K^{4n}\biggl[ \frac{(n+1)^3}{4\pi G^3 M_\mathrm{limit}^2} \biggr]^{n+1} \biggl[ \frac{G^{3(n+1)} M_\mathrm{tot}^{2(n+1)}}{K^{4n}} \biggr] </math>

 

<math>~=</math>

<math>~ \biggl[ \frac{(n+1)^3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2}\biggr]^{n+1} \, . </math>

Next, we demonstrate that this pair of parametric relations satisfies the virial theorem and, in so doing, demonstrate how <math>~r_a</math> and <math>~p_a</math> may be directly related to each other. Given that Hoerdt's chosen normalization radius and normalization pressure are defined in terms of <math>~K</math> and <math>~M_\mathrm{limit}</math>, we begin with the virial theorem derived above in terms of <math>~K</math> and <math>~M_\mathrm{limit}</math>, setting <math>~\gamma_g = (n+1)/n</math>.

<math>~P_e </math>

<math>~=</math>

<math>~K \biggl( \frac{3M_\mathrm{limit}}{4\pi R_\mathrm{eq}^3} \biggr)^{(n+1)/n} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{(n+1)/n}} - \biggl(\frac{3GM_\mathrm{limit}^2}{20\pi R_\mathrm{eq}^4} \biggr) \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} \, .</math>

After setting <math>~R_\mathrm{eq} = r_a R_\mathrm{Horedt} </math>, a bit of algebraic manipulation shows that the first term on the right-hand side of the virial equilibrium expression becomes,

<math>~ K \biggl( \frac{3M_\mathrm{limit}}{4\pi R_\mathrm{eq}^3} \biggr)^{(n+1)/n} \frac{\mathfrak{f}_A}{\mathfrak{f}_M^{(n+1)/n}} </math>

<math>~=</math>

<math>~ r_a^{-3(n+1)/n} \mathfrak{f}_A \biggl[ \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{n-3} \frac{(n+1)^{3n}}{(4\pi)^n}\biggr]^{(n+1)/[n(n-3)]} [K^{4n} G^{-3(n+1)} M_\mathrm{limit}^{-2(n+1)} ]^{1/(n-3)} \, , </math>

while the second term on the right-hand side becomes,

<math>~ \biggl(\frac{3GM_\mathrm{limit}^2}{20\pi R_\mathrm{eq}^4} \biggr) \frac{\mathfrak{f}_W}{\mathfrak{f}^2_M} </math>

<math>~=</math>

<math>~ \frac{3}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \cdot r_a^{-4} (4\pi)^{-(n+1)/(n-3)} (n+1)^{4n/(n-3)}~ [K^{4n} G^{-3(n+1)} M_\mathrm{limit}^{-2(n+1)} ]^{1/(n-3)} \, . </math>

But, using Horedt's expression for <math>~P_e</math>, the left-hand side of the virial equilibrium equation becomes,

<math>~P_e = p_a P_\mathrm{Hoerdt}</math>

<math>~=</math>

<math>~ p_a~(4\pi)^{-(n+1)/(n-3)} ~(n+1)^{3(n+1)/(n-3)} [K^{4n} G^{-3(n+1)} M_\mathrm{limit}^{-2(n+1)} ]^{1/(n-3)} \, . </math>

Hence, the statement of virial equilibrium is,

<math>~ p_a~ </math>

<math>~=</math>

<math>~ \biggr\{ r_a^{-3(n+1)/n} \mathfrak{f}_A \biggl[ \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{n-3} \frac{(n+1)^{3n}}{(4\pi)^n}\biggr]^{(n+1)/[n(n-3)]} </math>

 

 

<math>~~ - \frac{3}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \cdot r_a^{-4} (4\pi)^{-(n+1)/(n-3)} (n+1)^{4n/(n-3)} \biggr\}(4\pi)^{(n+1)/(n-3)} ~(n+1)^{-3(n+1)/(n-3)} </math>

 

<math>~=</math>

<math>~ \mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M \cdot r_a^3} \biggr)^{(n+1)/n} - \frac{3(n+1)}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \cdot r_a^{-4} \, ; </math>

or, multiplying through by <math>~r_a^4</math> and rearranging terms,

<math>~ \mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} r_a^{(n-3)/n} - p_a r_a^4 </math>

<math>~=</math>

<math>~ \frac{3(n+1)}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} \, . </math>

Now, Hoerdt has given analytic expressions for <math>~r_a</math> and <math>~p_a</math> in terms of the Lane-Emden function and its first derivative. The question is, what should the expressions for our structural form factors be in order for this virial expression to hold true for all pressure-truncated polytropic structures? As has been summarized above, in the case of an isolated polytrope, whose surface is located at <math>~\xi_1</math> and whose global properties are defined by evaluation of the Lane-Emden function at <math>~\xi_1</math>, we know that (see the above summary),

Structural Form Factors for Isolated Polytropes

<math>~\mathfrak{f}_M</math>

<math>~=</math>

<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\xi_1} </math>

<math>\mathfrak{f}_W </math>

<math>~=</math>

<math>~\frac{3^2\cdot 5}{5-n} \biggl[ \frac{\Theta^'}{\xi} \biggr]^2_{\xi_1} </math>

<math>\mathfrak{f}_A </math>

<math>~=</math>

<math> \frac{3(n+1) }{(5-n)} ~\biggl[ \Theta^' \biggr]^2_{\xi_1} </math>

These same expressions may or may not work for pressure-truncated polytropes, even if the evaluation radius is shifted from <math>~\xi_1</math> to <math>~\tilde\xi</math>. Let's see …

Inserting Hoerdt's expressions for <math>~r_a</math> and <math>~p_a</math> into the viral equilibrium expression, we have,

<math>~ \frac{3(n+1)}{5} \cdot \frac{\mathfrak{f}_W}{\mathfrak{f}_M^2} </math>

<math>~=</math>

<math>~ \mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} [ \tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)} ]^{(n-3)/n} ~-~ \tilde\theta_n^{n+1}( -\tilde\xi^2 \tilde\theta' )^{2(n+1)/(n-3)} [ \tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)} ]^{4} </math>

 

<math>~=</math>

<math>~ \mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} [ \tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)} ]^{(n-3)/n} ~-~ \tilde\theta_n^{n+1} \tilde\xi^4 [( -\tilde\xi^2 \tilde\theta' )^{2(n+1)+4(1-n)} ]^{1/(n-3)} </math>

 

<math>~=</math>

<math>~ \mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} [ \tilde\xi^{(n-3)} ( -\tilde\xi^2 \tilde\theta' )^{(1-n)} ]^{1/n} ~-~ \tilde\theta_n^{n+1} \tilde\xi^4 [( -\tilde\xi^2 \tilde\theta' )^{-2} ] </math>

 

<math>~=</math>

<math>~ \mathfrak{f}_A \biggl( \frac{3}{\mathfrak{f}_M} \biggr)^{(n+1)/n} \tilde\xi^{-(n+1)/n} ( -\tilde\theta' )^{(1-n)/n} ~-~ \frac{\tilde\theta_n^{n+1} }{( -\tilde\theta' )^{2} } \, . </math>

Assuming that the structural form factor, <math>~\mathfrak{f}_M</math>, has the same functional expression as in the case of isolated polytropes (but evaluated at <math>~\tilde\xi</math> instead of at <math>~\xi_1</math>), the virial relation further reduces to the form,

<math>~ \frac{\tilde\theta_n^{n+1} }{( -\tilde\theta' )^{2} } </math>

<math>~=</math>

<math>~ \mathfrak{f}_A \biggl( \frac{\tilde\xi}{- \tilde\theta'} \biggr)^{(n+1)/n} \tilde\xi^{-(n+1)/n} ( -\tilde\theta' )^{(1-n)/n} - \biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \frac{\tilde\xi^2}{(-\tilde\theta^')^2} \cdot \mathfrak{f}_W </math>

 

<math>~=</math>

<math>~ \frac{\mathfrak{f}_A}{(- \tilde\theta' )^2} - \biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \frac{\tilde\xi^2}{(-\tilde\theta^')^2} \cdot \mathfrak{f}_W </math>

<math>~ \Rightarrow~~~\tilde\theta^{n+1} </math>

<math>~=</math>

<math>~ \mathfrak{f}_A - \biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \tilde\xi^2 \cdot \mathfrak{f}_W </math>

<math>~ \Rightarrow~~~\frac{\mathfrak{f}_A - \tilde\theta^{n+1} }{\mathfrak{f}_W} </math>

<math>~=</math>

<math>~ \biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \tilde\xi^2 \, . </math>

While this does not give us individual expressions for the form factors, <math>~\mathfrak{f}_W</math> and <math>~\mathfrak{f}_W</math>, the expression derived for the ratio of the form factors makes sense because the term that has been subtracted from <math>~\mathfrak{f}_A</math> in the numerator on the lefthand side, that is, <math>\tilde\theta^{n+1}</math>, naturally goes to zero in the limit of <math>~\tilde\xi \rightarrow \xi_1</math>, producing the correct expression for the ratio, <math>\mathfrak{f}_A/\mathfrak{f}_W</math>, in isolated polytropes. In summary, then, we have,

Structural Form Factors for Pressure-Truncated Polytropes

<math>~\tilde\mathfrak{f}_M</math>

<math>~=</math>

<math>~ \biggl[ - \frac{3\Theta^'}{\xi} \biggr]_{\tilde\xi} </math>

<math>~ ~\frac{\tilde\mathfrak{f}_A - \tilde\theta^{n+1} }{\tilde\mathfrak{f}_W} </math>

<math>~=</math>

<math>~ \biggl[ \frac{(n+1)}{3\cdot 5} \biggr] \tilde\xi^2 </math>

Notice that, in an effort to differentiate them from their counterparts developed earlier for "isolated" polytropes, we have affixed a tilde to each of these three form-factors, <math>~\mathfrak{f}_i</math>.

Renormalization

Grunt Work

Returning to the dimensionless form of the virial expression and multiplying through by <math>~[-\chi_\mathrm{eq}/(3D)]</math>, we obtain,

<math> \chi_\mathrm{eq}^4 = \frac{B}{D} \chi_\mathrm{eq}^{4-3\gamma_g} - \frac{A}{D} \, , </math>

or, after plugging in definitions of the coefficients, <math>~A</math>, <math>~B</math>, and <math>~D</math>, and rewriting <math>~\chi_\mathrm{eq}</math> explicitly as <math>~R_\mathrm{eq}/R_\mathrm{norm}</math>,

<math>~\biggl( \frac{R_\mathrm{eq}}{R_\mathrm{norm}} \biggr)^4 </math>

<math>~=</math>

<math> \biggl(\frac{3}{4\pi}\biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g} \biggl( \frac{P_e}{P_\mathrm{norm}} \biggr)^{-1} \frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_M^{\gamma_g}} \biggl( \frac{R_\mathrm{eq}}{R_\mathrm{norm}} \biggr)^{4-3\gamma_g} - \frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2} \biggl( \frac{P_e}{P_\mathrm{norm}} \biggr)^{-1} \frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_M^2} \, .</math>

This relation can be written in a more physically concise form, as follows. First, normalize <math>~P_e</math> to a new pressure scale — call it <math>~P_\mathrm{ad}</math> — and multiply through by <math>~(R_\mathrm{norm}/R_\mathrm{ad})^4</math> in order to normalizing <math>~R_\mathrm{eq}</math> to a new length scale,<math>~R_\mathrm{ad}</math>:

<math>~\biggl( \frac{R_\mathrm{eq}}{R_\mathrm{ad}} \biggr)^4 </math>

<math>~=</math>

<math> \biggl(\frac{3}{4\pi}\biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g} \biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{P_e}{P_\mathrm{ad}} \biggr)^{-1} \frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_M^{\gamma_g}} \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{3\gamma_g}\biggl( \frac{R_\mathrm{eq}}{R_\mathrm{ad}} \biggr)^{4-3\gamma_g} </math>

 

 

<math> ~- \frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2} \biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_M^2} \biggl( \frac{P_e}{P_\mathrm{ad}} \biggr)^{-1} \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{4} \, , </math>

or,

<math>~\Chi_\mathrm{ad}^4 </math>

<math>~=</math>

<math> \biggl(\frac{3}{4\pi}\biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g} \biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{3\gamma_g} \frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_M^{\gamma_g}}\cdot \frac{\Chi_\mathrm{ad}^{4-3\gamma_g} }{\Pi_\mathrm{ad}} - \frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2} \biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{4} \frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_M^2} \cdot \frac{1}{\Pi_\mathrm{ad}} \, ,</math>

where,

<math>~\Chi_\mathrm{ad}</math>

<math>~\equiv</math>

<math>~\frac{R_\mathrm{eq}}{R_\mathrm{ad}} \, ,</math>

<math>~\Pi_\mathrm{ad}</math>

<math>~\equiv</math>

<math>~\frac{P_\mathrm{e}}{P_\mathrm{ad}} \, .</math>

By demanding that the leading coefficients of both terms on the right-hand-side of the expression are simultaneously unity — that is, by demanding that,

<math>~\biggl(\frac{3}{4\pi}\biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{\gamma_g} \biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{3\gamma_g} \frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_M^{\gamma_g}}</math>

<math>~=</math>

<math>~1 \, ,</math>

and,

<math>~\frac{3}{20\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2} \biggl( \frac{P_\mathrm{norm}}{P_\mathrm{ad}} \biggr) \biggl( \frac{R_\mathrm{norm}}{R_\mathrm{ad}} \biggr)^{4} \frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_M^2} </math>

<math>~=</math>

<math>~1 \, ,</math>

we obtain the expressions for <math>~R_\mathrm{ad}/R_\mathrm{norm}</math> and <math>~P_\mathrm{ad}/P_\mathrm{norm}</math> as shown in the following table.

Renormalization for Adiabatic (ad) Systems

<math>~\frac{R_\mathrm{ad}}{R_\mathrm{norm}}</math>

<math>~\equiv</math>

<math>~\biggl[ \frac{1}{5} \biggl( \frac{4\pi}{3} \biggr)^{\gamma_g-1} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2-\gamma_g} \frac{\tilde\mathfrak{f}_W}{\tilde\mathfrak{f}_A \cdot \tilde\mathfrak{f}_M^{2-\gamma_g}} \biggr]^{1/(4-3\gamma_g)} </math>

 

<math>~=</math>

<math>~ \biggl[ \frac{1}{5^n} \biggl( \frac{4\pi}{3}\biggr)\biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{n-1} \frac{\tilde\mathfrak{f}_W^n}{\tilde\mathfrak{f}_A^n \cdot \tilde\mathfrak{f}_M^{n-1}} \biggr]^{1/(n-3)} </math>

<math>~\frac{P_\mathrm{ad}}{P_\mathrm{norm}}</math>

<math>~\equiv</math>

<math>~ \biggl[ \tilde\mathfrak{f}_A^4 \cdot \biggl( \frac{3\cdot 5^3}{4\pi} \cdot \frac{\tilde\mathfrak{f}_M^2}{\tilde\mathfrak{f}_W^3} \biggr)^{\gamma_g} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2\gamma_g} \biggr]^{1/(4-3\gamma)} </math>

 

<math>~=</math>

<math>~ \biggl[ \tilde\mathfrak{f}_A^{4n} \biggl(\frac{3\cdot 5^3}{4\pi} \biggr)^{n+1} \biggl( \frac{\tilde\mathfrak{f}_M^2}{\tilde\mathfrak{f}_w^3} \biggr)^{n+1} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2(n+1)} \biggr]^{1/(n-3)} </math>

Using these new normalizations, we arrive at the desired, concise virial equilibrium relation, namely,

<math>~\Pi_\mathrm{ad} = \Chi_\mathrm{ad}^{-3\gamma_g} - \Chi_\mathrm{ad}^{-4}</math>

            <math>\Leftrightarrow</math>           

<math>~ \Pi_\mathrm{ad} = \Chi_\mathrm{ad}^{-3(n+1)/n} - \Chi_\mathrm{ad}^{-4}</math>

or,

<math>~~\Chi_\mathrm{ad}^{4-3\gamma_g} - \Pi_\mathrm{ad} \Chi_\mathrm{ad}^4 = 1</math>

            <math>\Leftrightarrow</math>           

<math>~\Chi_\mathrm{ad}^{(n-3)/n} - \Pi_\mathrm{ad} \Chi_\mathrm{ad}^4 = 1 \, .</math>

In Terms of Free-Energy Coefficients

Referring back to relations between our free-energy coefficients, as presented earlier, we note that,

<math>~\frac{R_\mathrm{ad}}{R_\mathrm{norm}}</math>

<math>~=</math>

<math>~\biggl( \frac{\mathcal{A}}{\mathcal{B}}\biggr)^{n/(n-3)} \, ,</math>

<math>~\frac{P_\mathrm{ad}}{P_\mathrm{norm}}</math>

<math>~=</math>

<math>~\frac{3}{4\pi} \biggl[ \frac{\mathcal{B}^{4n}}{\mathcal{A}^{3(n+1)}} \biggr]^{1/(n-3)} \, .</math>

Hence, we can write,

<math>~\Chi_\mathrm{ad}</math>

<math>~=</math>

<math>~\chi_\mathrm{eq} ~\biggl( \frac{\mathcal{B}}{\mathcal{A}}\biggr)^{n/(n-3)} \, ,</math>

<math>~\Pi_\mathrm{ad}</math>

<math>~=</math>

<math>~\mathcal{D} ~\biggl[ \frac{\mathcal{A}^{3(n+1)}}{\mathcal{B}^{4n}} \biggr]^{1/(n-3)} \, .</math>


In Terms of Horedt's Equilibrium Parameters

For later use it is also worth developing expressions for both <math>~\Chi_\mathrm{ad}</math> and <math>~\Pi_\mathrm{ad}</math> that are in terms of our structural form factors and Horedt's two dimensionless functions, <math>~r_a</math> and <math>~p_a</math>. (Adopting a unified notation, we will set <math>~\gamma_g \rightarrow (n+1)/n</math>.)

<math>~\Chi_\mathrm{ad} \equiv \frac{R_\mathrm{eq}}{R_\mathrm{ad}}</math>

<math>~=</math>

<math>~\frac{R_\mathrm{eq}}{R_\mathrm{Hoerdt}} \cdot \frac{R_\mathrm{Hoerdt}}{R_\mathrm{norm}} \cdot \frac{R_\mathrm{norm}}{R_\mathrm{ad}}</math>

 

<math>~=</math>

<math>~ r_a \cdot \biggl[ \frac{4\pi}{(n+1)^n} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)^{n-1} \biggr]^{1/(n-3)} \cdot \biggl[ 5^n \biggl( \frac{3}{4\pi} \biggr) \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}}\biggr)^{1-n} \frac{\tilde\mathfrak{f}_A^n}{\tilde\mathfrak{f}_W^n \cdot \tilde\mathfrak{f}_M^{1-n}} \biggr]^{1/(n-3)} </math>

<math>~\Rightarrow~~~\Chi_\mathrm{ad}^{n-3} </math>

<math>~=</math>

<math>~ 3 r_a^{n-3} \cdot \biggl[ \frac{5}{(n+1)} \cdot \frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_W} \biggr]^n \tilde\mathfrak{f}_M^{n-1} \, . </math>

And,

<math>~\Pi_\mathrm{ad} \equiv \frac{P_e}{P_\mathrm{ad}}</math>

<math>~=</math>

<math>~\frac{P_e}{P_\mathrm{Hoerdt}} \cdot \frac{P_\mathrm{Hoerdt}}{P_\mathrm{norm}} \cdot \frac{P_\mathrm{norm}}{P_\mathrm{ad}}</math>

 

<math>~=</math>

<math>~ p_a \cdot \biggl[ \frac{(n+1)^3}{4\pi} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{-2}\biggr]^{(n+1)/(n-3)} \cdot \biggl[ \tilde\mathfrak{f}_A^{-4n} \cdot \biggl( \frac{4\pi}{3\cdot 5^3} \cdot \frac{\tilde\mathfrak{f}_W^3}{\tilde\mathfrak{f}_M^2} \biggr)^{(n+1)} \biggl( \frac{M_\mathrm{limit}}{M_\mathrm{tot}} \biggr)^{2(n+1)} \biggr]^{1/(n-3)} </math>

<math>~\Rightarrow~~~\Pi_\mathrm{ad}^{n-3} </math>

<math>~=</math>

<math>~ p_a^{n-3}~ \tilde\mathfrak{f}_A^{-4n} \cdot \biggl[ \frac{(n+1)^3}{3\cdot 5^3} \biggl( \frac{\tilde\mathfrak{f}_W^3}{\tilde\mathfrak{f}_M^2} \biggr) \biggr]^{n+1} \, . </math>

Plugging in the expressions for <math>~r_a</math> and <math>~p_a</math>, as reprinted, for example, above, along with our deduced expressions for <math>~\mathfrak{f}_M</math> and <math>~\mathfrak{f}_A</math> (in terms of <math>~\mathfrak{f}_W</math>), these two relations become:

<math>~\Chi_\mathrm{ad}^{n-3} </math>

<math>~=</math>

<math>~ 3 \biggl[ \tilde\xi ( -\tilde\xi^2 \tilde\theta' )^{(1-n)/(n-3)} \biggr]^{n-3} \cdot \biggl[ \frac{5}{(n+1)} \cdot \frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_W} \biggr]^n \biggl[- \frac{3\tilde\theta^'}{\tilde\xi} \biggr]^{n-1} </math>

 

<math>~=</math>

<math>~ \tilde\xi^{[(n-3)+2(1-n)-(n-1)]} \cdot \biggl[ \frac{3\cdot 5}{(n+1)} \cdot \frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_W} \biggr]^n </math>

 

<math>~=</math>

<math>~ \biggl[ \frac{3\cdot 5}{(n+1)\tilde\xi^2} \cdot \frac{\tilde\mathfrak{f}_A}{\tilde\mathfrak{f}_W} \biggr]^n \, ; </math>

and,

<math>~\Pi_\mathrm{ad}^{n-3} </math>

<math>~=</math>

<math>~ \biggl[ \tilde\theta_n^{n+1}( -\tilde\xi^2 \tilde\theta' )^{2(n+1)/(n-3)} \biggr]^{n-3}~ \tilde\mathfrak{f}_A^{-4n} \cdot \biggl[ \frac{(n+1)}{3\cdot 5} \cdot \tilde\mathfrak{f}_W \biggr]^{3(n+1)} \biggl( \frac{3}{\tilde\mathfrak{f}_M}\biggr)^{2(n+1)} </math>

 

<math>~=</math>

<math>~ \tilde\theta_n^{(n+1)(n-3)}( -\tilde\xi^2 \tilde\theta' )^{2(n+1)} ~ \tilde\mathfrak{f}_A^{-4n} \cdot \tilde\xi^{-6(n+1)} \biggl[ \frac{(n+1)\tilde\xi^2}{3\cdot 5} \cdot \tilde\mathfrak{f}_W \biggr]^{3(n+1)} \tilde\xi^{2(n+1)} (-\tilde\theta^')^{-2(n+1)} </math>

 

<math>~=</math>

<math>~ \tilde\theta_n^{(n+1)(n-3)}~ \tilde\mathfrak{f}_A^{-4n} \cdot \biggl[ \frac{(n+1)\tilde\xi^2}{3\cdot 5} \cdot \tilde\mathfrak{f}_W \biggr]^{3(n+1)} \, . </math>

Summary

If we define,

<math>~a_\mathrm{ad}</math>

<math>~\equiv</math>

<math>~\frac{(n+1)\tilde\xi^2 }{3\cdot 5} \cdot \mathfrak{f}_W \, ,</math>     and,

<math>~b_\mathrm{ad}</math>

<math>~\equiv</math>

<math>~\tilde\theta^{n+1} \, ,</math>

in which case the relationship between <math>~\mathfrak{f}_A</math> and <math>~\mathfrak{f}_A</math> for pressure-truncated polytropes can be rewritten as,

<math>~\mathfrak{f}_A </math>

<math>~=</math>

<math>~a_\mathrm{ad} + b_\mathrm{ad} \, .</math>

In addition, the expressions for the dimensionless equilibrium radius and the dimensionless external pressure, as just derived, may be written as, respectively,

<math>~\Chi_\mathrm{ad}</math>

<math>~=</math>

<math>~ \biggl[ 1 + \frac{b_\mathrm{ad}}{a_\mathrm{ad}} \biggr]^{n/(n-3)} \, , </math>     and,

<math>~\Pi_\mathrm{ad} </math>

<math>~=</math>

<math>~ b_\mathrm{ad} \biggl[ \frac{a_\mathrm{ad}^{3(n+1)} }{( a_\mathrm{ad} + b_\mathrm{ad} )^{4n} } \biggr]^{1/(n-3)} = \frac{b_\mathrm{ad}}{a_\mathrm{ad}} \biggl[ 1 + \frac{b_\mathrm{ad}}{a_\mathrm{ad}} \biggr]^{-4n/(n-3)} \, . </math>

Using these expressions, it is easy to demonstrate that the virial equilibrium relation is satisfied, namely,

<math>~\Pi_\mathrm{ad} </math>

<math>~=</math>

<math>~\Chi_\mathrm{ad}^{-3(n+1)/n} - \Chi_\mathrm{ad}^{-4} \, .</math>

P-V Diagram

For an arbitrary value of the adiabatic exponent, <math>~\gamma_g</math>, it isn't possible to invert this virial relation to obtain an analytic expression for <math>~\chi_\mathrm{ad}</math> as a function of <math>~\Pi_\mathrm{ad}</math>. But, as written, the virial relation dictates the behavior of <math>~\Pi_\mathrm{ad}</math> as a function of <math>~\Chi_\mathrm{ad}</math>. Figure 4 displays this <math>~\Pi_\mathrm{ad}(\chi_\mathrm{ad})</math> behavior for a number of different values of <math>~\gamma_g</math>.

Figure 4: Equilibrium Adiabatic P-V Diagram

The curves shown here, on the right, trace out the function,

<math> ~\Pi_\mathrm{ad} = (\Chi_\mathrm{ad}^{4-3\gamma_g} - 1)/\Chi_\mathrm{ad}^4 \, , </math>

for six different values of <math>~\gamma_g</math> — specifically, for <math>2, ~5/3, ~7/5, ~6/5, ~1, ~2/3</math>, as labeled — and show the dimensionless external pressure, <math>~\Pi_\mathrm{ad}</math>, that is required to construct a nonrotating, self-gravitating, pressure-truncated adiabatic sphere with an equilibrium radius <math>~\Chi_\mathrm{ad}</math>. The solid red curve identifies the behavior of an isothermal <math>~(\gamma_g=1)</math> system. The mathematical solution becomes unphysical wherever the pressure becomes negative.

Equilibrium Adiabatic P-R Diagram


For physically relevant solutions, both <math>~\Chi_\mathrm{ad}</math> and <math>~\Pi_\mathrm{ad}</math> must be nonnegative. Hence, as is illustrated by the curves in Figure 4, the physically allowable range of equilibrium radii is,

<math> 1 \le \Chi_\mathrm{ad} \le \infty \, ~~~~~\mathrm{for}~ \gamma_g < 4/3 \, ; </math>

<math> 0 < \Chi_\mathrm{ad} \le 1 \, ~~~~~~\mathrm{for}~ \gamma_g > 4/3 \, . </math>

Each of the <math>~\Pi_\mathrm{ad}(\Chi_\mathrm{ad})</math> curves drawn in Figure 4 exhibits an extremum. In each case this extremum occurs at a configuration radius, <math>~\Chi_\mathrm{extreme}</math>, given by,

<math> \frac{\partial\Pi_\mathrm{ad}}{\partial\Chi_\mathrm{ad}} = 0 \, , </math>

that is, where,

<math> 4 - 3\gamma_g \Chi_\mathrm{ad}^{4-3\gamma_g} = 0 ~~~~\Rightarrow ~~~~~ \Chi_\mathrm{extreme} = \biggl[ \frac{4}{3\gamma_g} \biggr]^{1/(4-3\gamma_g)} \, . </math>

For each value of <math>~\gamma_g</math>, the corresponding dimensionless pressure is,

<math> ~\Pi_\mathrm{extreme} = \biggl(\frac{4}{3\gamma} - 1 \biggr) \biggl[ \frac{3\gamma_g}{4} \biggr]^{4/(4-3\gamma_g)} \, . </math>

In terms of the polytropic index, the equivalent limiting expressions are,

<math>~\Chi_\mathrm{extreme} = \biggl[ \frac{4n}{3(n+1)} \biggr]^{n/(n-3)}</math>

          and          

<math>~\Pi_\mathrm{extreme}^{(n-3)} = (4n)^{-4n} (n-3)^{n-3} [3(n+1)]^{3(n+1)} \, .</math>

(In a separate, related discussion of the free-energy function, we demonstrate that this "extremum" also serves as a dividing line between dynamically stable and unstable models along a given curve.)


In examining the group of plotted curves, notice that, for <math>~\gamma_g > 4/3</math>, an equilibrium configuration with a positive radius can be constructed for all physically realistic — that is, for all positive — values of <math>~\Pi_\mathrm{ad}</math>. Also, consistent with the behavior of the curves shown in Figure 4, the extremum arises in the regime of physically relevant — i.e., positive — pressures only for values of <math>~\gamma_g < 4/3</math>; and in each case it represents a maximum limiting pressure.



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Maximum Mass

<math>n=5</math> Polytropic

When <math>~\gamma_a = 6/5</math> — which corresponds to an <math>~n=5</math> polytropic configuration — we obtain,

<math> ~\Pi_\mathrm{max} = \Pi_\mathrm{ad}\biggr|_\mathrm{extreme}^{(\gamma_g = 6/5)} = \biggl( \frac{3^{18}}{2^{10}\cdot 5^{10}} \biggr) \, , </math>

which corresponds to a maximum mass for pressure-bounded <math>~n=5</math> polytropic configurations of,

<math>~M_\mathrm{max} = \Pi_\mathrm{max}^{1/2} \biggl(\frac{3\cdot 5^3}{2^2\pi} \biggr)^{1/2} \biggl( \frac{\bar{c_s}^8}{G^3 P_e} \biggr)^{1/2} = \biggl(\frac{3^{19}}{2^{12}\cdot 5^{7}\pi} \biggr)^{1/2} \biggl( \frac{\bar{c_s}^8}{G^3 P_e} \biggr)^{1/2} \, .</math>

This result can be compared to other determinations of the Bonnor-Ebert mass limit.

Whitworth's (1981) Isothermal Free-Energy Surface

© 2014 - 2021 by Joel E. Tohline
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Recommended citation:   Tohline, Joel E. (2021), The Structure, Stability, & Dynamics of Self-Gravitating Fluids, a (MediaWiki-based) Vistrails.org publication, https://www.vistrails.org/index.php/User:Tohline/citation