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SUBRAHMANYAN CHANDRASEKHAR

SUBRAHMANYAN CHANDRASEKHAR

  • Subrahmanyan Chandrasekhar was an Indian-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. The Chandrasekhar limit is named after him.
  • Chandrasekhar in distinct periods worked in various areas including stellar structure, theory of white dwarfs, stellar dynamics, theory of radiative transfer, quantum theory of the negative ion of Hydrogen, 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.                SUBRAHMANYAN CHANDRASEKHAR
  • During World War II, Chandrasekhar worked at the Ballistic Research Laboratories in Maryland. While there, he worked on problems of ballistics. Chandrasekhar’s expertise in hydrodynamics led Robert Oppenheimer to invite him to join the Manhattan Project at Los Alamos, but delays in the processing of his security clearance prevented him from contributing to the project.
  • Chandrasekhar developed a unique style of mastering several fields of physics and astrophysics; consequently, his working life can be divided into distinct periods. He would exhaustively study a specific area, publish several papers in it and then write a book summarizing the major concepts in the field. He would then move on to another field for the next decade and repeat the pattern.
  • Thus he studied stellar structure, including the theory of white dwarfs, during the years 1929 to 1939, and subsequently focused on stellar dynamics from 1939 to 1943. Next, he concentrated on the theory of radiative transfer and the quantum theory of the negative ion of hydrogen from 1943 to 1950.
  • This was followed by sustained work on hydrodynamic and hydromagnetic stability from 1950 to 1961. In the 1960s, he studied the equilibrium and the stability of ellipsoidal figures of equilibrium, and also general relativity.
  • During the period, 1971 to 1983 he studied the mathematical theory of black holes, and, finally, during the late 80s, he worked on the theory of colliding gravitational waves.
  • From 1952 to 1971 Chandrasekhar was editor of the Astrophysical Journal. He was awarded the Nobel Prize in Physics in 1983 for his studies on the physical processes important to the structure and evolution of stars.                                  SUBRAHMANYAN CHANDRASEKHAR
  • Chandrasekhar accepted this honor, but was upset that the citation mentioned only his earliest work, seeing it as a denigration of a lifetime’s achievement. He shared it with William A. Fowler.
  • Chandrasekhar’s most notable work was the astrophysical Chandrasekhar limit. In 1999, NASA named the third of its four “Great Observatories” after Chandrasekhar. This followed a naming contest which attracted 6,000 entries from fifty states and sixty-one countries.
  • The Chandra X-ray Observatory was launched and deployed by Space Shuttle Columbia on July 23, 1999. The Chandrasekhar number, an important dimensionless number of magnetohydrodynamics, is named after him. The asteroid 1958 Chandra is also named after Chandrasekhar.

Chandrasekhar limit

  • The Chandrasekhar limit is the maximum mass of a stable white dwarf star. The limit was first published by Wilhelm Anderson and E. C. Stoner, and was named after Subrahmanyan Chandrasekhar, the Indian-American astrophysicist who improved upon the accuracy of the calculation in 1930, at the age of 19.
  • This limit was initially ignored by the community of scientists because such a limit could only lead to the natural discovery of black holes, which were considered a scientific impossibility at the time. White dwarfs, unlike main sequence stars, resist gravitational collapse primarily through electron degeneracy pressure, rather than thermal pressure.
  • The Chandrasekhar limit is the mass above which electron degeneracy pressure in the star’s core is insufficient to balance the star’s own gravitational self-attraction.
  • Consequently, white dwarfs with masses greater than the limit undergo further gravitational collapse, evolving into a different type of stellar remnant, such as a neutron star or black hole. Those with masses under the limit remain stable as white dwarfs.                SUBRAHMANYAN CHANDRASEKHAR
  • The currently accepted value of the limit is about 1.44 solar masses ( 2.864 x 1030 kg).

Super-Chandrasekhar mass Supernovae

  • In April 2003, the Supernova Legacy Survey observed a type la supernova, designated SNLS-03D3bb, in a galaxy approximately 4 billion light years away. According to a group of astronomers at the University of Toronto and elsewhere, the observations of this supernova are best explained by assuming that it arose from a white dwarf which grew to twice the mass of the Sun before exploding.
  • They believe that the star, dubbed the “Champagne Supernova” by University of Oklahoma astronomer David R. Branch, may have been spinning so fast that centrifugal force allowed it to exceed the limit.
  • Alternatively, the supernova may have resulted from the merger of two white dwarfs, so that the limit was only violated momentarily. Nevertheless, they point out that this observation poses a challenge to the use of type la supernovae as standard candles.                              SUBRAHMANYAN CHANDRASEKHAR
  • Since the observation of the Champagne Supernova in 2003, more very bright type la supernovae are thought to have originated by white dwarfs whose masses exceeded the Chandrasekhar limit.
  • The super-Chandrasekhar mass white dwarfs that have originated these supernovae are believed to have had masses up to 2.4-2.8 solar masses. One way to potentially explain the problem of the Champagne Supernova was considering it the result of an aspherical explosion of a white dwarf.

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