S. Chandrasekhar was an Indian-born American astrophysicist who, with William A. Fowler, won the 1983 Nobel Prize for Physics for key discoveries that led to the currently accepted theory on the later evolutionary stages of massive stars. By the early 1930s, scientists had concluded that after converting all of their hydrogens to helium stars lose energy and contract under the influence of their own gravity. These stars, known as white dwarf stars, contract to about the size of 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 the eventual understanding of supernovas, neutron stars, and black holes. He did important work on energy transfer by radiation in stellar atmospheres and convention 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). 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), Truth and Beauty: Aesthetics and Motivations in Science (1987), and Newton’s Principia for the Common Reader(1995).