Editing Degenerate matter (section)

=== Neutron degeneracy <span class="anchor" id="neutron matter"></span> ===
<!-- This section is linked from [[Neutronium]] -->
{{main|Neutron star}}
Neutron degeneracy is analogous to electron degeneracy and exists in [[neutron star|neutron stars]], which are partially supported by the pressure from a degenerate neutron gas.<ref name="physics-of-neutron-stars">{{cite journal |title=The Physics of Neutron Stars |first=A. Y. |last=Potekhin |year=2011 |journal=Physics-Uspekhi |volume=53 |issue=12 |pages=1235–1256 |arxiv=1102.5735 |bibcode=2010PhyU...53.1235Y |doi=10.3367/UFNe.0180.201012c.1279 |s2cid=119231427 }}</ref> Neutron stars are formed either directly from the supernova of stars with masses between 10 and 25 ''M''<sub>☉</sub> ([[Solar mass|solar masses]]), or by [[white dwarf|white dwarfs]] acquiring a mass in excess of the [[Chandrasekhar limit]] of 1.44&nbsp;''M''<sub>☉</sub>, usually either as a result of a merger or by feeding off of a close binary partner. Above the Chandrasekhar limit, the gravitational pressure at the core exceeds the electron degeneracy pressure, and electrons begin to combine with protons to produce neutrons (via inverse [[beta decay]], also termed [[electron capture]]). The result is an extremely compact star composed of "nuclear matter", which is predominantly a degenerate neutron gas with a small admixture of degenerate proton and electron gases.

Neutrons in a degenerate neutron gas are spaced much more closely than electrons in an electron-degenerate gas because the more massive neutron has a much shorter [[Matter wave|wavelength]] at a given energy. This phenomenon is compounded by the fact that the pressures within neutron stars are much higher than those in white dwarfs. The pressure increase is caused by the fact that the compactness of a neutron star causes gravitational forces to be much higher than in a less compact body with similar mass. The result is a star with a diameter on the order of a thousandth that of a white dwarf.

The properties of neutron matter set an upper limit to the mass of a [[Neutron stars|neutron star]], the [[Tolman–Oppenheimer–Volkoff limit]], which is analogous to the [[Chandrasekhar limit]] for [[white dwarf]] stars.