Subrahmanyan Chandrasekhar, who died in 1995, was an astrophysical legend in his time. In astronomy he specialised in the role in football played by a sweeper: he would enter a new field previously ploughed by others and systematically pursue every twist and turn of the scientific ball. This typically led to a massive series of papers which culminated in a book that condensed, clarified and summarised the field, upon that he would turn to an entirely new topic. He repeated this procedure eight times in a working life that spanned 65 years. Stellar structure, stellar dynamics, radiative transfer, hydromagnetic stability, the stability of ellipsoidal figures of equilibrium and black holes: these were subjects that Chandra mastered, dominated for years, encapsulated in a masterly tome, and, apart from the last field, general relativity, the great love of his life, promptly abandoned.
From White Dwarfs to Black Holes: The Legacy of S. Chandrasekhar celebrates the many achievements of Chandra. The contributors include some of his collaborators, former students and colleagues, who collectively present a view of Chandra the scientist as well as Chandra the man. This book is a fitting tribute to Chandra's mastery of astrophysics, and to his well-merited status as an outstanding human being. It brings out, for instance, his wry sense of humour. He was proud of celebrating such facts as that, one year, the only two students who attended his general relativity course at the University of Chicago, to which he would have to make the long commute from Williams Bay, subsequently each received Nobel prizes. So of course did Chandra, one of the very few astrophysicists to join this select group.
All of his books were acknowledged masterpieces. The many papers he produced were almost always characterised by mathematical rigour in seemingly endless detail. Chandrasekhar's approach was invariably conservative. He would read exhaustively about the historical antecedents in a field and discover aspects that were either unaddressed or whose answers in the literature were unsatisfactory. He would then pose a question that he proceeded to answer incrementally, in so detailed a fashion that no stone was left unturned. When he was finished with a field, it was as though a plague of locusts had swept it clean of every blade of grass.
He viewed general relativity, the relativistic theory of gravitation, as the ultimate example of the mastery of beauty in nature by man, and not only in the realm of scientific achievement. He wrote a book, The Series Painting of Claude Monet and the Landscape of General Relativity , where he described how he found beauty in mathematical equations.
Chandra began as a realist. His choice of problems was rigorously required to be astrophysically relevant. But as time went on, his fascination with the mathematics underlying black holes gradually turned him more and more to seek mathematical elegance along with rigour, as the culmination of his efforts. It is fascinating to see how this great man went in a direction so different from that of his nemesis, Sir Arthur Eddington, himself the greatest astrophysicist of his time, the founder of modern astrophysics, and the host of Chandra when he arrived in Cambridge in 1930 to embark on the most creative and brilliant phase of his long and illustrious career.
Eddington hoped, vainly as it turned out, that some new physical theory, more fundamental than relativity, would come into play to avert what seemed to be a disaster for astronomy, and one not found in nature. Collapsed stars were singular objects, and an affront to nature, so Eddington asserted. Eddington did not believe the results of Chandra, who showed that a white dwarf above a certain mass would inevitably collapse. Driven as much by his philosophical views as by science, Eddington publicly refuted Chandra, but went on to devote much of his later research to a theory of physics that was so removed from reality that no one has since succeeded in penetrating its obscurantism.
Nor was this all. As E. E. Salpeter remarks in his contribution to the Chandrasekhar volume concerning Eddington's works on quantum mechanics and special relativity published in 1935:"On some level of consciousness Eddington must have known he had written nonsense - how could he live with himself and how could two respectable journals publish such papers?" Ironically, it was Eddington himself who first published in 1924 a mathematical solution of general relativity that was equivalent to the existence of the horizon that protects us from the space-time singularity at the centre of the black hole, but according to the contribution to this volume by Roger Penrose, "Eddington appeared not to appreciate what he had himself done".
In 1937, Chandra left Cambridge for the Yerkes Observatory of the University of Chicago, and remained associated with Chicago for the rest of his life. His work on stellar collapse foreshadowed the discovery of black holes, in all but name, by Oppenheimer and Snyder in 1939. Chandra decided to work on general relativity when he was nearly 60 years old. He turned back to the problem of stellar stability that he had initiated in the 1930s, and showed that inclusion of the general relativistic theory of gravitation led to qualitatively new effects. There was thought to be a new regime of stellar stability that had led to the prediction of super-massive stars, at an interesting moment in astronomy when quasars were first discovered.
However, Chandra soon showed that general relativity was fatal to the survival possibilities of a super-massive star. Collapse was inevitable, and super-massive black holes were an inevitable consequence.
This was a timely contribution and had a considerable impact on astronomy. Chandra went on to devote the rest of his life to studying the problem of gravitational radiation, which provides the only means by which we can ever hope to detect the formation of a black hole. It was a natural sequel, since his earlier fundamental work had inevitably led to the notions of black holes and singularities. Indeed the circle was closed. His later work did not lead to any profound insights but was driven by the quest for mathematical elegance, coupled with a deep belief in the ultimate simplicity of nature and the underlying connection between physics and mathematics, which may be characterised by his motivation for working on black holes: "The black holes of nature are the most perfect microcosmic objects there are in the universe... they are the simplest objects as well."
Joseph Silk is professor of astronomy, University of Oxford.
White Dwarfs to Black Holes: The Legacy of S. Chandrasekhar
Editor - G. Srinivasan
ISBN - 0 226 76996 8
Publisher - University of Chicago Press
Price - £31.95
Pages - 242