# Early Interactions with Vera Rubin

Note from Joel E. Tohline:  I doubt that she knew it, but Dr. Vera C. Rubin was a significant influence on my astronomy career. What follows are some highlights of my early professional interactions with her.

## Neighborhood Meeting at Yale University (1979)

Yale Neighborhood Meeting (1979)
For two years, beginning in the summer of 1978, I held a J. Willard Gibbs instructorship in the astronomy department at Yale University. In my first year, I was encouraged — along with another young astronomer, Dr. Carol A. Christian — to organize a so-called Neighborhood Meeting at Yale. The idea was to focus on a topic that would bring together faculty, postdocs and graduate students from universities and research centers that were "within driving distance" of the Yale campus; this, and limiting the gathering to 1½ days (just one overnight stay) would keep travel expenses to a minimum. We accepted the challenge. Given that, at that time, the astrophysics community, worldwide, was making significant progress on a number of issues related to galaxies — both observationally and theoretically — the topic we picked was …
Rotation: The Dynamical Structure of Galaxies
(A Neighborhood Meeting at Yale University)
Dates: 23 - 24 March 1979

Dr. Vera Rubin agreed to be our opening speaker. It was an opportunity for the (> 90) attendees to hear and see — first hand from the expert — how significant the evidence was for flat rotation curves. Five speakers followed: Dr. Jeremiah Ostriker (Princeton), Dr. Alar Toomre (MIT), Dr. Kevin Prendergast (Columbia University), Dr. Paul Schechter (Harvard-Smithsonian CfA), and Dr. Richard Miller (Chicago).

## Tohline Visits CIW:DTM (1980)

In early February, 1980, I visited the Carnegie Institution of Washington's Department of Terrestrial Magnetism (CIW:DTM) in Washington, DC to meet and interact with Vera Rubin and her research group. During that visit, I had the opportunity to present an informal talk in which I pitched the idea that flat rotation curves in galaxies might be explained by modifying Newton's law of gravity at large distances. This is the idea that I first presented in a formal manner in the summer of 1982 at the IAU Symposium No. 100.

## IAU Symposium No. 100 (1982)

An astronomical symposium sanctioned by the International Astronomical Union (IAU) titled, Internal Kinematics and Dynamics of Galaxies, was held in Besançon, France, August 9 - 13, 1982. This is the professional conference at which I presented a short "poster paper" titled, "Stabilizing a Cold Disk with a 1/r Force Law.". It appears as a two-page article that begins on p. 105 of the published symposium proceedings.

Dr. Rubin was (again!) the lead-off speaker for this five-day symposium; accordingly, the paper that she prepared for the symposium — titled, Systematics of HII Rotation Curves — appears as the first article (pp. 3 - 8) in the proceedings. Two pages of text (pp. 9 - 10) that immediately follow her article record six questions that were asked of Dr. Rubin at the end of her presentation, along with her six responses. The sixth question was from me; here is the published record:

 TOHLINE:   I would like to emphasize at the opening of this symposium that the often quoted ratio M/L is in fact the ratio V2r/L of the directly measurable quantities V, r and L. This ratio V2r/L can only be interpreted as an indicator of mass to light ratio if we assume that Newton's law of gravitational attraction is correct on the scale of galaxies. Since Keplerian behavior is essentially never seen in extra-galactic systems, I might be so bold as to suggest that the validity of Newton's law should now be seriously questioned. I hope that observers who have definitive evidence that Keplerian behavior has been observed in any system will emphasize that evidence at this meeting. RUBIN:   While we have observed that most Sa, Sb and Sc, galaxies have flat or slightly rising rotation curves, a few have slightly falling curves. However, I know of no isolated galaxy with rotation velocities decreasing as rapidly as $V \propto r^{-1 / 2}$. The point you raise is worth keeping in mind although I believe most of us would rather alter Newtonian gravitational theory only as a last resort.

## Rubin's Scientific American Article (1983)

Vera Rubin published a detailed description of the observational evidence for Dark Matter in Spiral Galaxies in the June, 1983 issue of Scientific American (pp. 96 - 108). An excerpt from near the bottom of p. 102 of that article reads,

 "Perhaps the most radical idea for explaining the observed high rotational velocities is one advanced independently by Joel E. Tohline of Louisiana State University and M. Milgrom and J. Bekenstein of the Weizmann Institute of Science. They have proposed that at great distances the Newtonian theory of gravitation must be modified, thereby allowing rotational velocities in galaxies to remain high at such distances from the galactic center even in the absence of unseen mass." -- Vera C. Rubin

This nod of recognition from Dr. Rubin broadened my visibility — both professionally and among the public — more than any other single citation. For example …

### Primack at UC, Santa Cruz

That same month (June 1983) I received a (hand-written) letter from Dr. Joel Primack (a physicist at UC, Santa Cruz) containing the following text:

 "I'm working on a review of dark matter for Annual Reviews (with Sandy Faber, George Blumenthal and Doug Lin) and would very much appreciate it if you would send me a copy of your paper on gravity weakening with distance as an explanation of constant rotation curves, referred to in Vera Rubin's recent Scientific American article… Please also send a copy to George Blumenthal at UC Santa Cruz. Thanks very much!" -- Joel Primack

Receiving this request from Joel Primack was exciting for me on two fronts: (1) Having my work cited in a high-quality review article would significantly enhance its visibility. (2) I had only recently (1978) earned my doctoral degree in astronomy from UC, Santa Cruz and had completed courses taught by both Sandy Faber and George Blumenthal, so I knew them well and was happy to hear that they had become aware of research endeavors that I was pursuing beyond the focus of my dissertation research.

### Princeton IAS

Postcard from Herbert Rood (1983)
Also, in late May of 1983, I received a postcard requesting reprints of my work from Dr. Herbert Rood (Princeton's Institute for Advanced Study). The letter that I wrote to him in response (dated 3 June 1983) contains the following text:
 "Dear Herbert:  Your recent request for reprints of my work on the non-Newtonian Force Law came as a bit of a shock. I was, until then, unaware that Vera had mentioned my work in her article — in fact, that issue of Scientific American only arrived to subscribers here at LSU the day that your request for reprints appeared in my mailbox."

Shortly thereafter I received a letter (dated 17 June 1983) from Dr. John N. Bahcall (also, Princeton's IAS) that began as follows …

 "Dear Joel:   Herb Rood showed me an abstract that you had written in which you consider some of the Solar system consequences of modifying the Newtonian force law." -- John N. Bahcall

Bahcall then asked whether or not I had considered how the standard mathematical expression of the virial theorem would be generalized in the context of my proposed non-Newtonian gravitational attraction. He derived what he considered to be the appropriate additional term that would be required, then applied the result to the case of "rich clusters" of galaxies. HIs conclusion was that my proposed modification of Newton's Law "… would overestimate the missing mass [in rich clusters] by a factor of 30" relative to what is observed. His reference regarding the relevant observational measurements was Neta Bahcall's article in Annual Review of Astronomy and Astrophysics (1977, Vol. 15, pp. 505 - 540).

I wrote back to John Bahcall, stating that I agreed with his derived correction to the virial theorem but that my interpretation of the published observational results — as found for example in Neta Bahcall's review article — was different from his. It looked to me as though the modified virial theorem expression nicely explains the mass-to-light ratio measurements in rich clusters. After studying my response, Dr. Bahcall wrote back:

 "… Thank you for your interesting letter on the r-1 force. You are indeed right that the mass to light ratio is typically 300 for rich clusters (I misquoted Neta's article). Thus there is no inconsistency with the virial equation I derived, provided one takes [a scale length] a ∼ 10 kpc … Very intriguing." -- John N. Bahcall

Over the subsequent couple of decades, John and Neta Bahcall visited LSU several times. As it turns out, John had graduated from high school in Shreveport, Louisiana, and he had a brother who lived in Baton Rouge.

## Exchange of Letters with Jim Felten (1984) … and Beyond

Draft of James E. Felten's (1984) paper
About half a year later, Dr. James E. Felten — at the time, a research scientist at the NASA Goddard Space Flight Center in Maryland — was discussing with Dr. Rubin the published work of Milgrom & Bekenstein and she told him that Joel Tohline "worked on 'Milgrom' ideas before Milgrom!" (See Felten's hand-written comment inside the red oval of the image shown here, on the right; click to make the thumbnail image larger.). I presume that Dr. Rubin was recalling the discussion that I had had with her group in early 1980. Dr. Felten then contacted me and we exchanged a few letters on the subject. Dr. Felten's critique of the Milgrom-Bekenstein work was published in The Astrophysical Journal (1984, 286, pp. 3-6); page 5 of this article includes a Note added in manuscript 1984 June 6 acknowledging these discussions.

In my (old-fashioned, paper) files, I have a record of insightful written exchanges that I had with a number of researchers throughout the decade of the 80s. For example …

• In the spring of 1985, I received a package of documents from Dr. Michael Disney (Cardiff, Wales). In addition to a wonderfully worded cover letter, the package contained a couple of thick draft articles in which he explored in a number of different directions what the implications would be of a modification to Newton's Law of the type I was proposing. He had not previously seen my work on this topic, but his thoughts were so in tune with my own that I was sure he had read my mind! It was wonderful to have heard from such a kindred spirit; his (draft) writings were like poetry, to me. Toward the end of the decade, at the invitation of Mike Disney and his astronomy colleagues at University College, Cardiff, I spent ten very enjoyable and intellectually stimulating days visiting Wales.
• In early 1986, Jeff Kuhn (Princeton, at the time) sent me a preprint of the paper he had written in collaboration with Kruglyak; he had heard of my work from Milgrom. A brief exchange of letters followed. An acknowledgement of my effort to examine the stability of cold stellar disks appears in their published paper (ApJ, 313, 1).