Degenerate matter

Degenerate Matter ( also: degenerate matter) is matter, mostly in the stars, so extreme has great density that quantum mechanical aspects play a role for them. Degeneracy means here that such matter can not be in a conventional manner, such as a classical ideal gas, describe. The term has nothing to do with degenerate energy levels.

Degenerate Fermionengas

If fermions ( eg protons, electrons or neutrons) are concentrated at extremely high density, a degeneracy pressure enters the gravity, which tries to increase the density yet, (also: Fermi pressure ) counter. The degeneracy pressure counteracts the gravitational pressure and has its origin in the Pauli exclusion principle, which forbids that two fermions can accept an identical quantum state at the same place at the same time. Therefore, a further compression would mean that fermions have to go into higher energy states.

Also, the ( quasi-) free (line) electron gas in ordinary metals is degenerate in this sense, that is, many metallic properties (such as electrical or thermal conductivity) can only be correctly described using quantum mechanics.

Degenerate matter into stars

White dwarfs are stabilized by the degeneracy pressure of their electron gas. In a physical binary star system can continue to grow a white dwarf through an accretion from its companion star. If its mass it reaches the Chandrasekhar limit, the degeneracy pressure can no longer compensate for the gravitational pressure. One might suspect, it would result in a neutron star. Instead, it is due to the rising temperature and density of new nuclear fusion reactions and there is a supernova of type Ia.