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(1910 - 1995)
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Subrahmanyan Chandrasekhar
Subrahmanyan Chandrasekhar

Subrahmanyan Chandrasekhar (or “Chandra”) was an Indian-American astrophysicist, best known for his work on the theoretical structure and evolution of stars, and particularly on the later evolutionary stages of massive stars and the calculation of the Chandrasekhar limit. He won the Nobel Prize in Physics (shared with William Fowler) in 1983 largely for this early work, although his research also covered many other areas within theoretical physics and astrophysics.

Padma Vibhushan Subrahmanyan Chandrasekhar was born on 19 October 1910 into a Tamil Hindu family in Lahore in the Punjab, British India (later Pakistan). His father was an accountant with the Indian railways as well as an accomplished Carnatic music violinist and musicologist; his mother was also an intellectual and is often credited with arousing Chandrasekhar's intellectual curiosity early on. His father's brother was the eminent physicist Chandrasekhara Venkata Raman who won the 1930 Nobel Prize in Physics for his work on the scattering of light and for the discovery of the so-called Raman effect of the scattering of photons.

Chandrasekhar was tutored at home initially, and later attended the Hindu High School in Triplicane, near Madras, from 1922 to 1925. Subsequently, he followed his illustrious uncle to study physics at Presidency College in Madras from 1925 to 1930, obtaining his BSc in 1930. Due to his academic achievements, he was awarded a Government of India scholarship to pursue graduate studies at the University of Cambridge, England, where he was admitted to Trinity College and became a research student of Professor Ralph Fowler. On the advice of another Cambridge professor of the period, Paul Dirac, Chandrasekhar also spent a year at the Institute of Theoretical Physics in Copenhagen, where he worked with Niels Bohr.

In 1933, he was awarded his PhD degree at Cambridge, and was elected to a Prize Fellowship at Trinity College for the period from 1933 to 1937, and it was during this time that he made acquaintances with the astrophysicists Sir Arthur Eddington and Arthur Milne. In 1936, he married Lalitha Doraiswamy, whom he had met initially during his time at Presidency College in Madras. Chandrasekhar considered her support and encouragement essential to his subsequent success, and they remained together for the rest of their long lives.

Perhaps Chandrasekhar's most famous success came very early in his career, as a young Fellow at Trinity College, with the publication of a series of papers between 1931 and 1935 on the “Chandrasekhar limit”. Building on the work his professor, Ralph Fowler, he calculated the maximum non-rotating mass which can be supported against gravitational collapse by electron degeneracy pressure. This limit describes the maximum mass of a white dwarf star, or, alternatively, the minimum mass above which a star will ultimately collapse into a neutron star or a black hole, following a supernova event, rather than remaining as a white dwarf. His calculations revealed that this was approximately 1.44 solar masses (1.44 times the mass of our Sun).

When he first proposed his Chandrasekhar limit, however, it was obstinately opposed by Sir Arthur Eddington, and Albert Einstein refused to believe that Chandrasekhar’s findings could result in a star collapsing down to a point. Much to Chandrasekhar's frustration, none of the other established physicists in Europe came to his rescue and, as a result of this disagreement with a man of the stature of Eddington, Chandrasekhar realized, with some bitterness, that his chances of obtaining a tenured position at a British university were slim at best.

So, when he received an offer of an assistant professorship at the University of Chicago faculty in early 1937, he decided to leave Cambridge and move to the United States. He was to remain at the University of Chicago for his entire remaining career, a total of 58 years. He became an associate professor in 1942, full professor in 1944, the Distinguished Service Professor of Theoretical Astrophysics in 1947, and attained emeritus status in 1985. He did some of his work at the University of Chicago’s Yerkes Observatory, and, later, at NASA’s Laboratory for Astrophysics and Space Research which was built at the University in 1966. During World War II, he worked at the Ballistic Research Laboratories at the Aberdeen Proving Ground in Maryland. He became a naturalized citizen of the United States in 1953.

Chandrasekhar’s working life can be divided into distinct periods, each period usually concluding with a book or monograph on the topic: he studied stellar structure, including the theory of white dwarfs, during the years 1929 to 1939 (summarized in his 1939 book “An Introduction to the Study of Stellar Structure”); he focussed on stellar dynamics from 1939 to 1943 (his book “Principles of Stellar Dynamics” was published in 1942); he concentrated on the theory of radiative transfer and the quantum theory of the negative ion of hydrogen from 1943 to 1950 (represented by another book, “Radiative Transfer”, published in 1950); he worked on hydrodynamic and hydromagnetic stability from 1950 to 1961 (his book “Hydrodynamic and Hydromagnetic Stability” was published in 1961); he studied the equilibrium and the stability of ellipsoidal figures of equilibrium, and also general relativity, during the 1960s (summarized in the book “Ellipsoidal Figures of Equilibrium” in 1968); during the period 1971 to 1983 he studied the mathematical theory of black holes (as described in his 1983 book “The Mathematical Theory of Black Holes”); and during the late 1980s he worked on the theory of colliding gravitational waves.

He was elected a Fellow of the Royal Society in 1944, and became an honorary member of the International Academy of Science in 1988. He was awarded numerous medals and prizes throughout his career, including the Bruce Medal (1952), the Gold Medal of the Royal Astronomical Society (1953), the National Medal of Science (1967), the Padma Vibhushan Medal (1968), the Henry Draper Medal (1971), the Copley Medal of the Royal Society (1984) and the Nobel Prize in Physics (1983). Although he accepted the honour of the Nobel Prize, he was somewhat upset that the citation (“for his theoretical studies of the physical processes of importance to the structure and evolution of the stars”) mentioned only his earliest work, seeing it as a denigration of a lifetime's achievement.

Chandrasekhar died of heart failure in Chicago on 21 August 1995, aged 84, and was survived by Lalitha, his wife of many years.

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