Placing Chandra's Work in Historical Context

Placing Chandra’s work in letters historical context

In the December 2010 issue of his result was incorrect, although it indi- adds that Fowler “offered to send it to PHYSICS TODAY, Freeman Dyson gave cated, fortuitously, the occurrence of a Edward Arthur Milne, who Fowler an interesting account (page 44) of Sub- limiting mass for white dwarfs. Then thought was more familiar with the rahmanyan Chandrasekhar’s role in Stoner, following Anderson’s observa- subject. After getting no response from 20th-century science. I enjoyed reading tion, obtained the exact relativistic equa- Fowler or Milne for months and seeing it, but the section concerning Chandra’s tion of state for degenerate electrons and no possibility of its publication in work on the limiting mass of white evaluated the complete density–mass re- Monthly Notices of the Royal Astronomical dwarfs and its early reception by Ralph lation in the approximation of uniform Society, Chandra sent it to the Astrophys- Fowler, Edward Arthur Milne, and density, finding an upper limit for the ical Journal on 12 November 1930; it was Arthur Eddington has several state- mass.2 A year earlier Frenkel also ob- published the following July.” ments, some often repeated in the past, tained the fully relativistic equation for a Wali further writes that “neither that contradict what publications and degenerate electron gas and applied it to Fowler nor Milne appreciated the star- correspondence at the time reveal.1,2 account for the extremely high density of tling discovery he [Chandra] had Dyson states that “Fowler had calcu- white dwarfs. Like Anderson, he found made.” Actually, when Fowler first met lated that for a given chemical compo- that for a white dwarf with a solar mass, Chandra, he told him that his “startling sition, the density of a white dwarf the electrons would become relativistic, discovery” had already been published would be proportional to the square of and he also found that in this case a so- by Stoner.2 Moreover, Milne promptly its mass.” Actually, in his 1926 seminal lution does not exist. Interestingly, for responded to Chandra by saying, “I paper Fowler did not present such a larger masses, Frenkel showed that the have been interested in your paper, it calculation; he only discussed the degeneracy pressure of ions could lead to seems very useful.... As regards pub- pressure-density relation of a degener- a solution with much higher density, of lication, I think that your paper might ate gas of electrons in the nonrelativistic order 1016 g/cm3, that now is known to well be accepted by R.A.S. for M. N.”4 limit.2 In that limit, the first physicist correspond to a neutron star. In February Finally, contrary to Dyson’s assertion who calculated the density of a white 1931, about the same time that Chandra that Chandra “received so little recog- dwarf model of uniform density with a wrote his paper, Lev Landau also ob- nition and acclaim at the time” for his solar mass was the Russian physicist tained the relativistic mass limit for white work, within four months after Chan- 2 Yakov Frenkel,3 who apparently was dwarfs but concluded that since stars dra presented his solution to the white unaware of Fowler’s paper. A year later with higher masses are observed, the dwarf problem, Henry Russell gave it a Edmund Stoner, a former student of laws of quantum mechanics must break positive evaluation; soon afterwards Ernest Rutherford’s at Cambridge Uni- down in such cases. Gerard Kuiper analyzed a recently versity, independently carried out the Dyson states that during Chandra’s found white dwarf to show that it same calculation showing explicitly the first voyage to England, “to his amaze- strongly favored Chandra’s result over dependence of the density on the ment, Chandra found that the change Eddington’s faulty analysis, and not square of the mass.2 The mean momen- from Newton to Einstein has a drastic much later other prominent as- tum of a degenerate gas of electrons is effect on the behavior of white dwarf tronomers came out in support of 2 proportional to the cube root of the den- stars.” But a letter to his father reveals Chandra’s work.5 sity, and Wilhelm Anderson, a physicist that Chandra already was aware of An- at the University of Tartu, Estonia, derson’s paper that had been published References pointed out that for white dwarfs with a year earlier. Moreover, Dyson states 1. W. Israel, Found. Phys. 26, 595 (1996). a solar mass, Stoner’s result was incon- that “Chandra finished his calculation 2. M. Nauenberg, J. Hist. Astron. 39, 297 sistent because the mean electron mo- before he reached England and never (2008), and references therein. mentum is of the order of its rest mass.2 had any doubt that his conclusion was 3. J. Frenkel, Z. Phys. 47, 819 (1928). Anderson attempted to calculate the correct.” But in a 1977 interview with 4. E. A. Milne to S. Chandrasekhar (2 No - relativistic pressure density relation, but Spencer Weart,2 Chandra admitted that vember 1930), in Subrahmanyan Chan- “at first I didn’t understand what this drasekhar Papers, Special Collections Research Center, University of Chicago limit meant and I didn’t know how it Regenstein Library. Letters are encouraged and should be would end.” Afterwards, Chandra sent by e-mail to [email protected] 5. F. Wesemael, Ann. Sci. 67, 205 (2010). wrote several papers with Milne that in- (using your surname as “Subject”), or by Michael Nauenberg troduced an ad hoc incompressible fi- ([email protected]) standard mail to Letters, PHYSICS TODAY, nite density at the core of the white American Center for Physics, One Physics University of California, Santa Cruz dwarf to allow the existence of such Ellipse, College Park, MD 20740-3842. In their engaging recollections of Please include your name, affiliation, stars for arbitrary large masses. Dyson Subrahmanyan Chandrasekhar’s ex- mailing address, e-mail address, and states that “when he arrived in Cam- traordinary career, neither Freeman daytime phone number on your attach- bridge and showed his results to ment or letter. You can also contact us Fowler, Fowler was friendly but . . . un- Dyson nor Kamesh Wali mention that online at http://www.physicstoday.org/ willing to sponsor Chandra’s paper for Chandra was the third person, not the pt/contactus.jsp. We reserve the right to publication.” In a biographical portrait first, to publish a white dwarf mass edit submissions. of Chandra, in the same issue of limit that involved a relativistic treat- PHYSICS TODAY (page 38), Kamesh Wali ment of degenerate electrons. Chandra

8 July 2011 Physics Today www.physicstoday.org