degeneracy pressure

[dĭ-jĕn′ər-ə-sē]

A pressure exerted by dense material consisting of fermions (such as electrons in a white dwarf star). This pressure is explained in terms of the Pauli exclusion principle, which requires that no two fermions be in the same quantum state. The more densely fermions are packed together and must share the same space, the more they must differ from each other in terms of their momentum. In turn, the greater the range in momentum, the greater the fraction of particles with high momentum, and these exert pressure on their surroundings. See also neutron star white dwarf.