1.6. The roads part

Tempted by a wealth of interests and prospects, the fathers of the `swirling hotch-potch' theory were not very resolute about raising their yet-unrisen-to-its-feet brainchild. Goldreich had no plans at all to continue working on spiral structure, and once he had moved from Cambridge to California in the summer of 1964 he did not pursue their studies. In the late 1970s only did he return to the subject, and then only when he began to study planetary ring dynamics with Tremaine (Goldreich & Tremaine 1978, 1979, 1980).

"You must appreciate that I was not a major player in the story you are concerned with nor did I ever consider myself to be one. Moreover, I am not a particularly scholarly scientist, and am undoubtedly guilty of paying too little attention to who deserves credit and for what even on topics to which I have contributed. My main pleasure comes from understanding things for myself. I like to get applause for my work, but that is a secondary benefit." (Goldreich)

No sooner had Lynden-Bell submitted the GLB article (spring 1964) than he "just finished a paper (Lynden-Bell 1965a) on explaining the bending of the galactic plane by a precession of the galaxy" and then "temporarily left spiral research for a problem in general relativity" (Lynden-Bell 1964a) - apparently, not without a compunction on Goldreich's departure and partial unsuccess of arranging things with Toomre so that they "can work complementarily rather than on the same topics" (Lynden-Bell 1964c). "I quite expect to stop or rather remained stopped for a bit" regarding galaxy-disk problems, Lynden-Bell wrote to the latter (Lynden-Bell 1964d), still in winter 1964-65 he collaborated with Ostriker on a general energy principle for differentially rotating bodies. In his 1960 thesis (Lynden-Bell 1960) he already had one for axisymmetric modes, and he was eager now about the non-axisymmetric case envisaging its relevance to spiral modes. The work was almost completed by the time Lynden-Bell left Cambridge, and his summer 1965 arrival at the Royal Greenwich Observatory in Herstmonceux returned him for a while to spiral regeneration channels. Impressed by the "formidable difficulties" that the leading spiral theories of the day met "in fitting precisely the observed phenomena in our Galaxy", he announced that he was to show "a fundamental role for a small magnetic field in a basically gravitational theory" via "modification of the Goldreich-Lynden-Bell-Toomre approach". That, he believed, "provides a more natural discrimination between old stars and gas, avoids the relaxation difficulties and provides condensations which do not spin too rapidly for star formation." (Lynden-Bell 1966, p.57-58)

"I have gone over to being a magnetic man in part", Lynden-Bell wrote to Toomre (Lynden-Bell 1965b) inviting him for a bigger joint effort, which struck the latter as a bizarre digression (Toomre). Something must have been disturbing him as to which spiral ideas to believe. ²⁵ Possibly, this was partly due to his general motif of finding pleasure in formulating and trying original dynamical problems rather than in routinely clearing roads already laid. There Lynden-Bell was no doubt successful since despite his few miscarriages (like Lynden-Bell 1965a) he had won fame as a galaxy dynamicist already in the 1960s, especially after his important studies on violent relaxation of stellar systems (Lynden-Bell 1967) and on the nature of quasars (Lynden-Bell 1969). With all that he himself has admitted, as if implying the reverse of the medal:

"I have no claim to the theory of spiral structure. Of those who once worked on it I feel that I am one of those least well informed as to its current state and most skeptical that a full understanding has even yet been reached." (Lynden-Bell)

Working with Toomre on stellar wakes, Julian prepared his PhD thesis "On the Enhancement of the Random Velocities of Stars in Disk-like Galaxies", supervised officially by Lin and submitted in August 1965 (Julian 1965). ²⁶ There and in his consequent paper (Julian 1967) he calculated the heating of orbiting stars such wakes cause. The simple truth of local differential rotation and triaxial residual-velocity ellipsoid had long argued partial relaxation of our Galaxy's star disk but - paradoxically - found no reasonable explanation in terms of two-star encounters (see Chandrasekhar 1942). In the early 1950s, Spitzer & Schwarzschild (1951, 1953) proposed and qualitatively estimated the heating by giant `molecular complexes'. Now Julian included collective star interactions and found much higher growth rates and velocity-dispersion points: taking the `complex' mass of an order of 10⁶ - 10⁷ suns, he had Toomre's Q -parameter grown to as large as 2.0 or so. ²⁷ This disfavored the Lin-Shu wave picture ensured by the capabilities of marginally stable disks, yet no reasonable reduction of Julian's generous choice for a typical gas-cloud mass was seen to let Q go under 1.4.

As a PhD-degree holder, Julian worked at the University of Chicago until 1967 when he got a postdoc position at Caltech. Goldreich warmly met him there and had him running and swimming during lunch the second day already. Soon they went on to do their famous work on pulsar electrodynamics (Goldreich & Julian 1969). For a while, Julian kept a side interest in the continuing discussion between his distinguished former MIT colleagues, but when Toomre wrote to him in 1970 musing about possible "large-scale sequels to the JT paper", Julian - now in New Mexico - "seemed to be not at all interested" (Toomre).

²⁵ "I still do not know whether the magnetism is an important catalyst for the modes we see or whether it is irrelevant. It is irrelevant for a purely stellar system but what we see has gas and star-formation." (Lynden-Bell) Back.

²⁶ "Bill throughout our mutual involvement remained C.C.'s student officially. [...] When I returned to MIT in fall 1963, C.C. himself had urged me to look after Bill, not on the grounds that he wasn't talented but because - to C.C.'s own taste, at least - he seemed too independent." (Toomre) Back.

²⁷ Following Julian, Thorne (1968) solved an inverse problem of dynamical friction on a massive particle in a slightly eccentric orbit in a hot thin disk of stars. With JT techniques, he included collective stellar interactions whose neglect had been excused for pairwise stellar encounters in elliptical galaxies and galaxy clusters where Jeans' length is of the order of the whole system, but not in flat galaxies where it was co-ordered with their thickness, pointing at much more pronounced collective effects. Thorne found that this collective play could double the friction in magnitude. Back.