Editing Gravitational collapse (section)

===Neutron star===
{{Main|Neutron star}}
Neutron stars are formed by the gravitational collapse of the cores of larger stars. They are the remnant of supernova types [[Type Ib supernova|Ib]], [[Type Ic supernova|Ic]], and [[Type II supernova|II]]. Neutron stars are expected to have a skin or "atmosphere" of normal matter on the order of a millimeter thick, underneath which they are composed almost entirely of closely packed neutrons called [[neutron matter]]<ref>{{Cite journal |last1=Gandolfi |first1=Stefano |last2=Gezerlis |first2=Alexandros |last3=Carlson |first3=J. |date=2015-10-19 |title=Neutron Matter from Low to High Density |url=https://www.annualreviews.org/doi/10.1146/annurev-nucl-102014-021957 |journal=Annual Review of Nuclear and Particle Science |language=en |volume=65 |issue=1 |pages=303–328 |doi=10.1146/annurev-nucl-102014-021957 |issn=0163-8998|arxiv=1501.05675 |bibcode=2015ARNPS..65..303G }}</ref> with a slight dusting of free electrons and protons mixed in. This degenerate neutron matter has a density of about {{val|6.65|e=17|u=kg/m3}}.{{sfn|Carroll|Ostlie|2017|p=578}}

The appearance of stars composed of [[exotic matter]] and their internal layered structure is unclear since any proposed [[equation of state]] of [[degenerate matter]] is highly speculative. Other forms of hypothetical degenerate matter may be possible, and the resulting [[quark star]]s, [[strange star]]s (a type of quark star), and [[preon star]]s, if they exist, would, for the most part, be indistinguishable from a [[neutron star]]: In most cases, the [[exotic matter]] would be hidden under a crust of "ordinary" degenerate neutrons. {{Citation needed|date=September 2020}}