Subrahmanyan Chandrasekhar

Subrahmanyan Chandrasekhar (19 October 1910 – 21 August 1995) was an Indian-American theoretical physicist who spent his professional life in the United States.

Chandrasekhar was born in Lahore on 19 October 1910 of the British Raj (present-day Pakistan) in a Tamil Brahmin family, to Sita Balakrishnan (1891–1931) and Chandrasekhara Subrahmanya Ayyar (1885–1960) who was stationed in Lahore as Deputy Auditor General of the Northwestern Railways at the time of Chandrasekhar's birth.

He had two elder sisters, Rajalakshmi and Balaparvathi, three younger brothers, Vishwanathan, Balakrishnan, and Ramanathan, and four younger sisters, Sarada, Vidya, Savitri, and Sundari.

His paternal uncle was the Indian physicist and Nobel laureate Chandrasekhara Venkata Raman.

His mother was devoted to intellectual pursuits, had translated Henrik Ibsen's A Doll's House into Tamil and is credited with arousing Chandra's intellectual curiosity at an early age.

The family moved from Lahore to Allahabad in 1916, and finally settled in Madras in 1918.

Chandrasekhar was tutored at home until the age of 12.

In middle school his father taught him mathematics and physics and his mother taught him Tamil.

He later attended the Hindu High School, Triplicane, Madras during the years 1922–25.

Subsequently, he studied at Presidency College, Madras (affiliated to the University of Madras) from 1925 to 1930, writing his first paper, "The Compton Scattering and the New Statistics", in 1929 after being inspired by a lecture by Arnold Sommerfeld.

He obtained his bachelor's degree, BSc (Hon.), in physics, in June 1930.

In July 1930, Chandrasekhar was awarded a Government of India scholarship to pursue graduate studies at the University of Cambridge, where he was admitted to Trinity College, secured by R. H. Fowler with whom he communicated his first paper.

During his travels to England, Chandrasekhar spent his time working out the statistical mechanics of the degenerate electron gas in white dwarf stars, providing relativistic corrections to Fowler's previous work (see Legacy below).

In his first year at Cambridge, as a research student of Fowler, Chandrasekhar spent his time calculating mean opacities and applying his results to the construction of an improved model for the limiting mass of the degenerate star.

At the meetings of the Royal Astronomical Society, he met E. A. Milne.

At the invitation of Max Born he spent the summer of 1931, his second year of post-graduate studies, at Born's institute at Göttingen, working on opacities, atomic absorption coefficients, and model stellar photospheres.

On the advice of P. A. M. Dirac, he spent his final year of graduate studies at the Institute for Theoretical Physics in Copenhagen, where he met Niels Bohr.

After receiving a bronze medal for his work on degenerate stars, in the summer of 1933, Chandrasekhar was awarded his PhD degree at Cambridge with a thesis among his four papers on rotating self-gravitating polytropes.

On 9 October, he was elected to a Prize Fellowship at Trinity College for the period 1933–1937, becoming only the second Indian to receive a Trinity Fellowship after Srinivasa Ramanujan 16 years earlier.

He had been so certain of failing to obtain the fellowship that he had already made arrangements to study under Milne that autumn at Oxford, even going to the extent of renting a flat there.

During this time, Chandrasekhar became acquainted with British physicist Sir Arthur Eddington.

Eddington took an interest in his work, but in January, 1935, gave a talk severely criticizing Chandrasekhar's work (see and Chandrasekhar–Eddington dispute).

In 1935, Chandrasekhar was invited by the director of the Harvard Observatory, Harlow Shapley, to be a visiting lecturer in theoretical astrophysics for a three-month period.

He travelled to the United States in December.

During his visit to Harvard, Chandrasekhar greatly impressed Shapley, but declined his offer of a Harvard research fellowship.

At the same time, Chandrasekhar met Gerard Kuiper, a noted Dutch astrophysical observationalist who was then a leading authority on white dwarfs.

Kuiper had recently been recruited by Otto Struve, the director of the Yerkes Observatory in Williams Bay, Wisconsin, which was run by the University of Chicago, and the university's president, Robert Maynard Hutchins.

Having known of Chandrasekhar, Struve was then considering him for one of three faculty posts in astrophysics, along with Kuiper; the other opening had been filled by Bengt Stromgren, a Danish theorist.

He was on the faculty at Chicago from 1937 until his death in 1995 at the age of 84, and was the Morton D. Hull Distinguished Service Professor of Theoretical Astrophysics.

A long-time professor at the University of Chicago, he did some of his studies at the Yerkes Observatory, and served as editor of The Astrophysical Journal from 1952 to 1971.

He was awarded the 1983 Nobel Prize in physics along with William A. Fowler for "...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 and black holes.

Many concepts, institutions, and inventions, including the Chandrasekhar limit and the Chandra X-Ray Observatory, are named after him.

Chandrasekhar worked on a wide variety of problems in physics during his lifetime, contributing to the contemporary understanding of stellar structure, white dwarfs, stellar dynamics, stochastic process, radiative transfer, the quantum theory of the hydrogen anion, hydrodynamic and hydromagnetic stability, turbulence, equilibrium and the stability of ellipsoidal figures of equilibrium, general relativity, mathematical theory of black holes and theory of colliding gravitational waves.

At the University of Cambridge, he developed a theoretical model explaining the structure of white dwarf stars that took into account the relativistic variation of mass with the velocities of electrons that comprise their degenerate matter.

He showed that the mass of a white dwarf could not exceed 1.44 times that of the Sun – the Chandrasekhar limit.

Chandrasekhar revised the models of stellar dynamics first outlined by Jan Oort and others by considering the effects of fluctuating gravitational fields within the Milky Way on stars rotating about the galactic centre.

His solution to this complex dynamical problem involved a set of twenty partial differential equations, describing a new quantity he termed "dynamical friction", which has the dual effects of decelerating the star and helping to stabilize clusters of stars.

Chandrasekhar extended this analysis to the interstellar medium, showing that clouds of galactic gas and dust are distributed very unevenly.

Chandrasekhar studied at Presidency College, Madras (now Chennai) and the University of Cambridge.