Electron degeneracy pressure occurs when electrons are compressed into a very small volume. Since their positions are well-known, they gain a large momentum in accordance with Heisenberg's uncertainty principle. This momentum creates a pressure which is temperature-independent and can result in helium flash in stars. Electron degeneracy pressure also supports white dwarf stars, and has magnitude

where is h-bar, is the mass of the electron, is the mass of a proton, is the density, and is the ratio of electrons to protons.

Chandrasekhar Limit, Electron, Fermion Degeneracy Pressure, White Dwarf