Neutron stars before 1967 and my debt to Chandra

Abstract

At least in his later years, Chandra was particularly famous for General Relativity, and throughout his brilliant career he was a model of mathematical rigor and elegance. I have never had a strong interest in General Relativity, I am mathematically about as sloppy as one can get away with and I have spent little time in Chicago. Because of this orthogonality, I have probably had less overlap with Chandrasekhar than most theoretical astrophysicists, and yet even in my case he has had a strong influence. I will illustrate this with a purely personal essay on my own work on equations of state and compact objects, especially neutron stars. It is interesting to speculate on why some topics are studied when they are, and I have put “neutron stars before 1967” in the title, because the reasons for ‘why’ are clear after 1967: Pulsars were discovered (Hewish et al. 1968), it became clear that they are rotating neutron stars (Gold 1968) and radiation mechanisms were discussed even just before the discovery (Pacini 1967). In the 40 years before this, on the other hand, there were few practical reasons to study neutron stars, except for the prescient suggestion of neutron stars in supernova remnants (Baade & Zwicky 1934). When I was a graduate student in the 1940s I was unaware of this paper, but my interest was aroused in a very indirect way by the earlier controversy between Chandrasekhar and Eddington on the equation of state for relativistic white dwarf stars. In astrophysics circles this controversy is usually described in terms of Eddington as a great man with deep philosophical beliefs and unorthodox views on how the laws of science might change — i.e., it was not clear whether he was morally right in “putting down” a young man so thoroughly and consistently, but it was not clear either till much later that he was scientifically wrong. However, in 1946 I was a graduate student in physics, not in astrophysics, my thesis advisor was Rudolf Peierls and it was clear that Eddington was wrong right from the start! At least this was the situation with two very specific papers of Eddington’s. These two papers (Eddington 1935a and 1935b) were mainly concerned with the laws of physics in existence at the time, especially quantum mechanics and special relativity, not with philosophy or the future (in one of them there was one delightful digression into the “magic numbers” in astronomy and physics which was vintage Eddington, but this did not impinge on the main text). There were two aspects to these papers: (i) they pointed out genuine difficulties that would be faced if one wanted to carry out very rigorous and very accurate calculations, and (ii) an explicit calculation of the equation of state for relativistic electrons as Fermi-Dirac particles which not only gave the wrong result but consisted of sheer nonsense or double-talk or both! An example of (i) was how to treat Dirac electrons under high pressure,