History
What is a White Dwarf
How Are White Dwarfs Formed
What Happens if Chandrasekhar Limit is Exceeded
Neutron Degeneracy beyond Chandrasekhar Limit
The value of the Chandrasekhar Limit was also calculated in 1932 by Lev Davidovich Landau, a Soviet physicist who, however, did not apply it to white dwarfs. However, at their inception, they are very hot and bright. But, having no inherent source of energy, gradually, they become cool by radiating energy. At very low temperatures, they are reduced to cold black dwarfs. White dwarfs are composed of electron degenerate matter, a Physics term for a collection of non-interacting electrons having pressure and other physical properties determined by quantum mechanics. Neutron stars are celestial bodies made of a collection of neutrons. Their average density is approximately the same as that of atomic nuclei. After low and medium mass stars lose their hydrogen fusing ability, they expand into heavenly bodies known as red giants. If the latter does not possess enough mass to generate temperatures of the order of 1 billion K to fuse carbon, an inert mass of carbon and oxygen accumulates at its center. Gradually, it sheds off its peripheral layers to give rise to planetary nebula and the core forms a white dwarf.
The Role of Electron Degeneracy Pressure in White Dwarf Formation
White dwarfs are supported from further collapse by electron degeneracy pressure. Electron degeneracy, like neutron degeneracy, is an application of Pauli Exclusion Principle to stars. It states that no two electrons having the same spin can occupy the same quantum state. When the lowest energy state is filled, the electrons are forced to occupy higher energy states resulting in a gain of speed. Such great speeds give rise to the said pressure that restricts the compression of matter into smaller volumes. This phenomenon can stop the continuing collapse of a super Chandrasekhar Limit white dwarf by giving rise to a neutron star. But for masses greater than 3 solar masses, even that would fail. This, in turn, leads to the formation of a black hole. In this connection, it may be mentioned that if neutron stars become more massive than 3 solar masses, they too can degenerate into black holes. https://en.wikipedia.org/wiki/Chandrasekhar_limit http://www.space.com/23756-white-dwarf-stars.html https://science.nasa.gov/astrophysics/focus-areas/black-holes/ https://www.nationalgeographic.com/science/article/white-dwarfs
