Subrahmanyan Chandrasekhar

Anyone asking who was Subrahmanyan Chandrasekhar must begin in Lahore, then part of British India, where he was born on October 19, 1910, the third of ten children in a Tamil Brahmin family ^[1]. His father, Chandrasekhara Subrahmanya Ayyar, worked as an officer in the Indian audit and accounts service attached to the railways, and his mother, Sitalakshmi, translated Henrik Ibsen into Tamil and pushed her children toward intellectual ambition ^[2]. Science ran in the family: his paternal uncle was C. V. Raman, who would win the 1930 Nobel Prize in Physics for the scattering effect that bears his name ^[1].

The family moved to Madras (now Chennai) in 1918, and the boy was tutored at home before entering Hindu High School in Triplicane. He enrolled at Presidency College, Madras, where he first studied physics and where, still an undergraduate, he published a paper on the Compton effect in the Proceedings of the Royal Society in 1929 ^[2]. A meeting with the visiting German physicist Arnold Sommerfeld introduced him to the new Fermi-Dirac statistics, mathematics that would soon shape his most famous work ^[3].

He completed his bachelor's degree in June 1930 and won a Government of India scholarship for graduate study at the University of Cambridge. He was nineteen years old when he boarded a ship for England that July ^[1].

During the long sea passage from Bombay to England in the summer of 1930, Chandrasekhar occupied himself with a calculation. Ralph Fowler at Cambridge had explained white dwarf stars, the dense remnants of ordinary stars, using the quantum mechanical pressure of degenerate electrons. Chandrasekhar asked what would happen if the electrons inside a very massive white dwarf moved at speeds approaching that of light, where Einstein's relativity changes the arithmetic ^[3].

The answer startled him. Once relativistic effects were included, degeneracy pressure could no longer resist gravity in stars above a certain mass, roughly 1.4 times the mass of the Sun in the modern value. A white dwarf heavier than this threshold could not exist; a dying star above the limit had to keep collapsing ^[3]. This boundary is now known as the Chandrasekhar limit, and it stands among the most consequential single results in twentieth century astrophysics, since it implied that nature must produce objects far stranger than white dwarfs ^[4].

At Cambridge he worked under Fowler, spent a formative year with Max Born in Göttingen and Niels Bohr's circle in Copenhagen, and received his PhD in 1933. That October, Trinity College elected him to a Prize Fellowship, an honor that had gone to only one other Indian before him, the mathematician Srinivasa Ramanujan ^[2].

The most painful episode of Chandrasekhar's career came on January 11, 1935, at a meeting of the Royal Astronomical Society in London. He had refined his white dwarf theory into a full account of stellar collapse and presented the results with confidence. Immediately afterward, Sir Arthur Eddington, the most celebrated astrophysicist of the age and a man Chandrasekhar regarded as a mentor, rose and mocked the work, declaring that there should be a law of nature to prevent a star from behaving in such an absurd way ^[4].

Eddington's objection had no sound mathematical basis, and leading physicists including Wolfgang Pauli and Paul Dirac privately told Chandrasekhar that his relativistic treatment was correct. Yet none would challenge Eddington publicly, and the dispute effectively pushed the young scientist out of the field of stellar structure for a time ^[4]. Chandrasekhar summarized his side of the argument in his 1939 monograph An Introduction to the Study of Stellar Structure, then deliberately moved on to other problems ^[5].

Decades later the verdict of physics was unambiguous. The collapse Eddington ridiculed is exactly what produces neutron stars and black holes, and the episode is often cited as a case study in how authority can delay the acceptance of correct science ^[4].

In 1936 Chandrasekhar returned briefly to India to marry Lalitha Doraiswamy, a fellow physics student from his Presidency College days. The couple then sailed for the United States, where he had accepted a position at the University of Chicago's Yerkes Observatory in Williams Bay, Wisconsin ^[1]. He joined the faculty in January 1937 and remained a University of Chicago scientist for the rest of his life, becoming Morton D. Hull Distinguished Service Professor in 1952 ^[2].

His working method became legendary. Roughly once a decade he would select a broad subject, master it completely, publish a systematic series of papers, distill the whole field into an authoritative book, and then abandon it for something new. In this fashion he produced classic monographs on stellar dynamics (1942), radiative transfer (1950), hydrodynamic and hydromagnetic stability (1961), ellipsoidal figures of equilibrium (1969), and the mathematical theory of black holes (1983) ^[5].

During the Second World War he contributed to ballistics research at the Aberdeen Proving Ground in Maryland. From 1952 to 1971 he edited The Astrophysical Journal, transforming a house organ of the University of Chicago into the leading journal of the field, a role he performed with exacting, sometimes feared, editorial standards ^[2]. He and Lalitha became American citizens in 1953 ^[1].

Honors accumulated steadily among Subrahmanyan Chandrasekhar achievements. He was elected a Fellow of the Royal Society in 1944, received its Royal Medal in 1962 and its Copley Medal in 1984, and was awarded the United States National Medal of Science in 1966 ^[2]. The Government of India conferred the Padma Vibhushan, its second highest civilian award, in 1968 ^[6].

The Nobel Prize in Physics arrived in 1983, shared with William A. Fowler. The Nobel committee cited Chandrasekhar for his theoretical studies of the physical processes important to the structure and evolution of stars, recognition that reached back to the white dwarf work he had begun on shipboard more than half a century earlier ^[7]. He was reportedly disappointed that the citation emphasized his earliest research, since he viewed his life's work as a connected whole rather than a single youthful discovery ^[4].

He never stopped producing. His 1983 treatise The Mathematical Theory of Black Holes became the standard reference on the subject, and in his final years he turned to the history of science, publishing Newton's Principia for the Common Reader in 1995, a line by line reconstruction of Newton's geometric proofs ^[5].

Chandrasekhar, known to colleagues simply as Chandra, cultivated a formal, disciplined style: precise speech, dark suits, and a punishing work schedule. For years he drove the roughly hundred miles between Yerkes Observatory and the Chicago campus to teach a small graduate course; among the students in one such class were Tsung-Dao Lee and Chen Ning Yang, who went on to win the 1957 Nobel Prize in Physics ^[2].

His marriage to Lalitha lasted nearly six decades, and he credited her patient support as the foundation of his career. The couple had no children. Outside physics he read widely in literature and reflected on aesthetics in science, themes he gathered in his 1987 essay collection Truth and Beauty ^[5].

He formally retired in 1980 but kept working daily. On August 21, 1995, Chandrasekhar died of heart failure in Chicago at the age of 84 ^[1]. Lalitha Chandrasekhar survived him by many years, dying in 2013 at the age of 102 ^[6].

Any Subrahmanyan Chandrasekhar biography ends with a sky full of his ideas. The Chandrasekhar limit is a working number in astronomy: it sets the mass scale for Type Ia supernovae, the standard candles used to measure the expansion of the universe, and it marks the dividing line beyond which collapsing stars form neutron stars or black holes ^[3].

In 1999 NASA launched its most powerful X-ray telescope and named it the Chandra X-ray Observatory in his honor, noting that the shortened form of his name means moon or luminous in Sanskrit ^[8]. The observatory has since imaged the hot remnants of exactly the kinds of stellar explosions his equations foretold. An asteroid, 1958 Chandra, also carries his name ^[6].

His influence persists through people as well as theorems. Across a Chicago career of nearly sixty years he supervised around fifty doctoral students, and the ten dense monographs he left behind are still consulted as definitive treatments of their subjects ^[2]. Among basic Subrahmanyan Chandrasekhar facts, perhaps the most telling is this: the calculation dismissed as absurd in 1935 is now taught in every undergraduate astrophysics course on Earth ^[4].