Chandrasekhar, Subrahmanyan


Chandrasekhar, Subrahmanyan (1910-1995), American theoretical astrophysicist and Nobel laureate, who contributed greatly to the current understanding of stellar evolution. He was born in Lahore, India (now Pakistan), and was educated in India and at Trinity College, University of Cambridge, earning a Ph.D. in 1933. In 1953 he became a U.S. citizen.


Although Chandrasekhar worked on theories of radiative transfer and convective transport of heat in stellar atmospheres, his most important studies concerned the small, dim, hot, dense stars known as white dwarfs (see Star). He determined that a star with a mass more than 1.44 times that of the mass of the sun cannot directly become a white dwarf, a limit now called the Chandrasekhar limit. He shared the Nobel Prize for physics in 1983 with U.S. physicist William A. Fowler for his work on stars. His books include An Introduction to the Study of Stellar Structure (1939) and Principles of Steller Dynamics (1942). The Chandra X-ray Observatory, a powerful telescope that the United States plans to launch into Earth’s orbit as a satellite in 1999, was named after Chandrasekhar.



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Chandrasekhar, Subrahmanyan




born Oct. 19, 1910, Lahore, India [now in Pakistan]

died Aug. 21, 1995, Chicago, Ill., U.S.




Indian-born American astrophysicist who, with William A. Fowler, won the 1983 Nobel Prize for Physics for formulating the currently accepted theory on the later evolutionary stages of massive stars.



Chandrasekhar was the nephew of Sir Chandrasekhara Venkata Raman, who won the Nobel Prize for Physics in 1930. Chandrasekhar was educated at Presidency College, at the University of Madras, and at Trinity College, Cambridge.From 1933 to 1937 he held a position at Trinity.



By the early 1930s, scientists had concluded that, after converting all of their hydrogen to helium, stars lose energy and contract under the influence of their own gravity. Thesestars, known as white dwarf stars, contract to about the size of the Earth, and the electrons and nuclei of their constituent atoms are compressed to a state of extremely high density. Chandrasekhar determined what is known as the Chandrasekhar limit—that a star having a mass more than 1.44 times that of the Sun does not form a white dwarf but instead continues to collapse, blows off its gaseous envelope in a supernova explosion, and becomes a neutron star. An even more massive star continues to collapse and becomes a black hole. These calculations contributed to theeventual understanding of supernovas, neutron stars, and black holes.



Chandrasekhar joined the staff of the University of Chicago, rising from assistant professor of astrophysics (1938) to Morton D. Hull distinguished service professor of astrophysics (1952), and became a U.S. citizen in 1953. He did important work on energy transfer by radiation in stellar atmospheres and convection on the solar surface.He also attempted to develop the mathematical theory of black holes, describing his work in The Mathematical Theory of Black Holes (1983).



Chandrasekhar was awarded the Gold Medal of the Royal Astronomical Society in 1953 and the Royal Medal of the Royal Society in 1962. His other books include An Introduction to the Study of Stellar Structure (1939), Principles of Stellar Dynamics (1942), Radiative Transfer (1950), Hydrodynamic and Hydromagnetic Stability (1961), and Truth and Beauty: Aesthetics and Motivations in Science (1987).





Additional reading



Kameshwar C. Wali, Chandra: A Biography of S. Chandrasekhar (1991), describes his life and career.






Chandrasekhar limit




in astrophysics, maximum mass theoretically possible for a stable white dwarf star.



This limiting value was named for the Indian-born astrophysicist Subrahmanyan Chandrasekhar, who formulated it in 1930. Using Albert Einstein's special theory of relativity and the principles of quantum physics, Chandrasekhar showed that it is impossible for a white dwarf star, which is supported solely by a degenerate gas of electrons, to be stable if its mass is greater than 1.44 times the mass of the Sun. If such astar does not completely exhaust its thermonuclear fuel, then this limiting mass may be slightly larger.



All direct mass determinations of actual white dwarf stars have resulted in masses less than the Chandrasekhar limit. A star that ends its nuclear-burning lifetime with a mass greater than the Chandrasekhar limit must become either a neutron star or a black hole.