Chandrasekhar limit
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The Chandrasekhar limit, also known as Schenberg-Chandrasekhar limit, is the maximum mass of a white dwarf, a type of star, and is approximately 3 × 1030 kg, around 1.44 times the mass of the Sun. This number is a bit different in various articles, from 1.2 to 1.46 times the mass of the Sun and depends on the chemical composition of the star. The limit was first discovered and calculated by the Indian physicist Subrahmanyan Chandrasekhar, working with the Brazilian physicist Mário Schenberg.
The heat generated by a star due to nuclear fusion of atoms of lighter elements into heavier ones pushes the atmosphere of the star out. As the star runs out of fuel the atmosphere collapses back on the star's core, pulled by the star's own gravity. If the star has a mass below the Chandrasekhar limit this collapse is limited by electron degeneracy pressure, which results in a stable white dwarf. If the star has a mass above the Chandrasekhar limit it has sufficient gravity to collapse past the white dwarf stage and become a neutron star, black hole, or possibly a theoretical quark star. If a stable white dwarf in a binary system with a giant star accretes enough material to exceed the Chandrasekhar limit, the star collapses and becomes a type Ia supernova. The remnant of the collapse is unlikely to be a neutron star as the explosion is violent enough to rip the white dwarf clean apart, leaving no star at all.
The Chandrasekhar limit arises from taking account of the effects of quantum mechanics in considering the behaviour of the electrons providing the degeneracy pressure supporting the white dwarf. Electrons, being fermions, cannot be at equal energy levels, so that, when an electron gas is cooling down, it is impossible for them to be given all minimal energy. Plenty of electrons will have to stay at higher energy levels and will thus give a certain pressure, which is purely quantum mechanical in its nature.
In the classical approximation a white dwarf may be arbitrarily massive with its volume inversely proportional to its mass. In the quantum mechanical calculation the typical energies to which degeneracy pressure forces the electrons in a massive white dwarf are non-negligible relative to their rest masses and a limiting mass emerges for a self-gravitating, spherically symmetric body supported by degeneracy pressure.
When Chandrasekhar first proposed his ideas, he was vehemently opposed by the British physicist Arthur Eddington. Embittered, Chandrasekhar moved to the United States where he remained at the University of Chicago for the most part. Although Eddington was subsequently proven wrong, Chandrasekhar was magnanimous in his victory.
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