Chandrasekhar , Subrahmanyan

(1910–1995) Indian–American astrophysicist

Chandrasekhar, who was born in Lahore, which is now in Pakistan, studied at the Presidency College, Madras, gaining his MA in 1930. He then went to Cambridge University, England, where in 1933 he both obtained his PhD and was elected to a fellowship. In 1936 he moved to America and has worked since 1937 at the University of Chicago and the Yerkes Observatory, serving as the Morton D. Hull Distinguished Service professor of Theoretical Astrophysics from 1952 to 1986, and as professor emeritus from 1986. He became an American citizen in 1953.

Chandrasekhar's major fields of study were stellar evolution and stellar structure and the processes of energy transfer within stars. It was known that stars could end their life either dramatically and explosively as a supernova or as an extremely small dense star of low luminosity known as a white dwarf. But what decided the particular path a star took was answered by Chandrasekhar in his Introduction to the Study of Stellar Structure (1939). He showed that when a star has exhausted its nuclear fuel, an inward gravitational collapse will begin. This will eventually be halted in most stars by the outward pressure exerted by a degenerate gas, i.e. a gas that is completely ionized, with the electrons stripped away from the atomic nuclei, and that is very highly compressed. The star will therefore have shrunk into an object composed of material so dense that a matchbox of it would weigh many tons.

Chandrasekhar showed that such a star would have the unusual property that the larger its mass, the smaller its radius. There will therefore be a point at which the mass of a star is too great for it to evolve into a white dwarf. He calculated this mass to be 1.4 times the mass of the Sun. This has since become known as theChandrasekhar limit. A star lying above this limit must either lose mass before it can become a white dwarf or take a different evolutionary path. In support of Chandrasekhar's theoretical work, it has been established that all known white dwarfs fall within the predicted limit.

In the 1970s Chandrasekhar devoted much time to the mathematical theory of black holes. He later made a detailed study of Newton's work and published his results in his Newton's Principia for the Common Reader.

For his numerous contributions to astrophysics, Chandrasekhar shared the 1983 Nobel Prize for physics with William Fowler.