Subrahmanyan Chandrasekhar was an Indian American astrophysicist who was awarded the 1983 Nobel Prize for Physics with William A. Fowler "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 best current theoretical models of the later evolutionary stages of massive star and black holes. The Chandrasekhar limit is named after him. Chandrasekhar worked on a wide variety of astrophysical problems in his lifetime, contributing to the contemporary understanding of stellar structure, white dwarves, stellar dynamics, radiative transfer, the quantum theory of the hydrogen anion, hydrodynamic and hydromagnetic stability, 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 University of Cambridge. He spent most of his career at the University of Chicago, spending some time in its Yerkes Observatory, and serving as editor of The Astrophysical Journal from 1952 to 1971. He served on the University of Chicago faculty from 1937 until his death in 1995 at the age of 84. Chandrasekhar married Lalitha Doraiswamy in September 1936. He had met her as a fellow student at Presidency College, Madras. Chandrasekhar was the nephew of Sir Chandrasekhara Venkata Raman, who was awarded the Nobel Prize for Physics in 1930. He became a naturalized citizen of the United States in 1953.