| definition |
Highly compressed matter in which the normal atomic structure has broken down and
which, because of quantum-mechanical effects, exerts a pressure that is independent
of temperature. Bodies with masses less than Chandrasekhar's limit (1.4 solar masses)
are supported by electron degeneracy pressure and have densities of about 10^6 kg/m^3.
In collapsed stars of mass above 1.4 solar masses, gravity will overwhelm electron
degeneracy and further collapse ensues. Electrons combine with protons to form neutrons,
so producing a neutron star. Because neutrons, like electrons, are fermions and therefore
subject to the Pauli exclusion principle, at high enough densities, about 10^14 kg/m^3,
neutron degeneracy pressure prevents further collapse of the star. For masses larger
than 2-3 solar masses, even neutron degeneracy cannot prevent further collapse, and
a black hole is formed.
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