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However, neutron degeneracy pressure is not by itself sufficient to hold up an object beyond 0.7 M ☉ and repulsive nuclear forces play a larger role in supporting more massive neutron stars. Neutron stars are partially supported against further collapse by neutron degeneracy pressure, a phenomenon described by the Pauli exclusion principle, just as white dwarfs are supported against collapse by electron degeneracy pressure. Most of the basic models for these objects imply that neutron stars are composed almost entirely of neutrons (subatomic particles with no net electrical charge and with slightly larger mass than protons) the electrons and protons present in normal matter combine to produce neutrons at the conditions in a neutron star. Once formed, they no longer actively generate heat, and cool over time however, they may still evolve further through collision or accretion. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past white dwarf star density to that of atomic nuclei. Neutron stars have a radius on the order of 10 kilometres (6 mi) and a mass of about 1.4 solar masses. white holes, quark stars, and strange stars), neutron stars are the smallest and densest currently known class of stellar objects. Except for black holes and some hypothetical objects (e.g.
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Radiation from the rapidly spinning pulsar PSR B1509-58 makes nearby gas emit X-rays (gold) and illuminates the rest of the nebula, here seen in infrared (blue and red).Ī neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich.