Subrahmanyan Chandrasekhar

A boy in Lahore, in a family of physicists

Subrahmanyan Chandrasekhar was born on the 19th of October, 1910, in Lahore, then part of British India. He was the third of ten children in a Tamil Brahmin household. His uncle was Chandrasekhara Venkata Raman, the Calcutta physicist who would win the 1930 Nobel for the scattering effect that still carries his name. Physics in the family was not abstract. It was the thing the famous uncle did.

Taught at home until age twelve, by his late teens he was already publishing short notes in The Indian Journal of Physics. In 1930 he took a first-class first from Presidency College, Madras, with a Government of India scholarship in hand for Cambridge.

A calculation on the deck of a steamship

In July 1930 he boarded the SS Pilsna in Bombay for the three-week passage to Venice. He was nineteen. In his luggage were Eddington’s The Internal Constitution of the Stars and Ralph Fowler’s 1926 paper on the white dwarf, which argued that those strange dim stars, mass roughly the Sun’s but radius roughly the Earth’s, were held up against gravity by the degeneracy pressure of their electrons. Fowler used nonrelativistic quantum statistics. Chandrasekhar, on the deck of the Pilsna, asked the obvious question. What happens when the electrons inside a white dwarf are squeezed so hard that they move at speeds close to the speed of light?

The relativistic correction changed the equation of state. Pressure no longer rose fast enough with density to resist gravity at arbitrary mass. There was a ceiling. Above a critical mass, no stable cold configuration existed. Chandrasekhar finished the calculation before Venice, refined it through 1935, and published a value of roughly 1.4 solar masses. Anything heavier, having exhausted its nuclear fuel, must continue collapsing past the white dwarf stage. The implication, which he stated in print and which no senior figure in 1931 was willing to take seriously, was that very massive stars must end as something stranger. The word “neutron star” did not yet exist. The phrase “black hole” was forty years away.

Subrahmanyan Chandrasekhar (19 October 1910 – 21 August 1995) was an Indian-American theoretical physicist. He shared the 1983 Nobel Prize in Physics "for his theoretical studies of the physical processes of importance to the structure and evolution of the stars." His mathematical treatment of stellar evolution yielded many of the current theoretical models of the later evolutionary stages of massive stars. The Chandrasekhar limit describes the maximum mass of a white dwarf (1.44 solar masses).…

The Eddington humiliation

On the 11th of January, 1935, Chandrasekhar presented the completed mass limit at a meeting of the Royal Astronomical Society in London. He spoke for fifteen minutes and sat down. Arthur Eddington, the most celebrated astrophysicist alive, the man whose textbook had taught Chandrasekhar the subject, stood up next. Eddington told the meeting that the relativistic equation of state was nonsense, that “there should be a law of Nature to prevent a star from behaving in this absurd way,” and that the young man’s calculation was a reductio ad absurdum of relativistic degeneracy itself. The room laughed. Chandrasekhar was not given a chance to reply.

He was twenty-four. Léon Rosenfeld and Wolfgang Pauli privately told him afterwards that Eddington was wrong and the calculation was right. None of them said so in public. The dispute simmered for years. Eddington never recanted. Chandrasekhar moved on to other problems, partly because arguing with Eddington in print was a career he did not want to have. He would say, decades later, that he learned from it never to overinvest emotionally in a single result.

Yerkes, Chicago, and a lifetime of monographs

In 1937 Chandrasekhar accepted a position at the University of Chicago’s Yerkes Observatory in Williams Bay, Wisconsin. He stayed at Chicago for the rest of his life and became a US citizen in 1953. He commuted through Wisconsin snow to teach a graduate seminar that for one famous winter had only two students enrolled: Tsung-Dao Lee and Chen Ning Yang. Both went on to share the 1957 Nobel Prize.

Chandrasekhar’s mode was to pick an area of theoretical astrophysics, exhaust it across a decade, publish a definitive monograph, and move on. An Introduction to the Study of Stellar Structure (1939) covered the white dwarf work begun on the Pilsna. Principles of Stellar Dynamics (1942), Radiative Transfer (1950), Hydrodynamic and Hydromagnetic Stability (1961), and Ellipsoidal Figures of Equilibrium (1969) each capped a phase. Students remembered the textbooks as the most demanding they had ever read. From 1952 to 1971 he was the managing editor of The Astrophysical Journal, reading every manuscript personally.

The Nobel, fifty-three years late

In 1983 the Royal Swedish Academy awarded him the Nobel Prize in Physics, shared with William Fowler, “for his theoretical studies of the physical processes of importance to the structure and evolution of the stars.” The committee was, in effect, citing the work of 1930. He was seventy-three. By then the mass limit had been renamed in his honour. The same year he published The Mathematical Theory of Black Holes, a 700-page analytical treatment of Kerr and Reissner-Nordström solutions, done in the style of the nineteenth-century masters he admired.

He died of a heart attack on the 21st of August, 1995, at the University of Chicago Medical Center, aged eighty-four. In 1999 NASA launched its third Great Observatory, the Chandra X-ray Observatory, named for him. It still orbits the Earth and still returns the data on accreting compact objects whose existence his 1931 ceiling first demanded.

What he means to the quantum story

Chandrasekhar is the figure who showed that the quantum world has astronomical consequences. The Pauli exclusion principle, written down a few years earlier as a rule about electrons in atoms, sets the mass at which a star must finally fail. The same statistics that build the periodic table also draw a line, a little above the Sun, beyond which gravity wins forever.