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It is a manifestation of the more general phenomenon of quantum degeneracy pressure. The term "degenerate" here is not related to degenerate energy levels, but to Fermi–Dirac statistics close to the zero-temperature limit [1] (temperatures much smaller than the Fermi temperature, which for metals is about 10000 K.)
While degeneracy pressure usually dominates at extremely high densities, it is the ratio between degenerate pressure and thermal pressure which determines degeneracy. Given a sufficiently drastic increase in temperature (such as during a red giant star's helium flash ), matter can become non-degenerate without reducing its density.
Conversely, two or more different states of a quantum mechanical system are said to be degenerate if they give the same value of energy upon measurement. The number of different states corresponding to a particular energy level is known as the degree of degeneracy (or simply the degeneracy) of the level.
This pressure is known as the degeneracy pressure. In this sense, systems composed of fermions are also referred as degenerate matter . Standard stars avoid collapse by balancing thermal pressure ( plasma and radiation) against gravitational forces.
The Chandrasekhar limit is a consequence of competition between gravity and electron degeneracy pressure. Electron degeneracy pressure is a quantum-mechanical effect arising from the Pauli exclusion principle. Since electrons are fermions, no two electrons can be in the same state, so not all electrons can be in the minimum-energy level.
In the case of degenerate energy levels, we can write the partition function in terms of the contribution from energy levels (indexed by j) as follows: =, where g j is the degeneracy factor, or number of quantum states s that have the same energy level defined by E j = E s.
In quantum mechanics, the Kramers' degeneracy theorem states that for every energy eigenstate of a time-reversal symmetric system with half-integer total spin, there is another eigenstate with the same energy related by time-reversal. In other words, the degeneracy of every energy level
Quantum-mechanical electron degeneracy pressure in a block of copper [83] 48 GPa Detonation pressure of pure CL-20, [84] the most powerful high explosive in mass production 69 GPa 10,000,000 psi Highest water jet pressure attained in research lab [85] 96 GPa Pressure at which metallic oxygen forms (960,000 bar) [81] 10 11 Pa