Editing Quark star (section)

==Formation==
[[File:TOV solution neutron quark star mass radius diagram.png|thumb|upright=1.75|Mass–radius relations for models of a neutron star with no exotic states (red) and a quark star (blue)<ref>F. Douchin, P. Haensel, ''A unified equation of state of dense matter and neutron star structure'', "Astron. Astrophys." 380, 151 (2001).</ref>]]
It is hypothesized that when the [[neutron-degenerate matter]], which makes up [[neutron star]]s, is put under sufficient pressure from the star's own [[gravity]] or the initial [[supernova]] creating it, the individual [[neutron]]s break down into their constituent [[quark]]s ([[up quark]]s and [[down quark]]s), forming what is known as quark matter. This conversion may be confined to the neutron star's center or it might transform the entire star, depending on the physical circumstances. Such a star is known as a quark star.<ref name="Shapiro">{{cite book |last1=Shapiro |first1=Stuart L. |last2=Teukolsky |first2=Saul A. |title=Black Holes, White Dwarfs and Neutron Stars: The Physics of Compact Objects |publisher=Wiley |year=2008 |isbn=978-0471873167}}</ref><ref>{{cite book |editor-last1=Blaschke |editor-first1=David |editor-first2=Armen |editor-last2=Sedrakian |editor-first3=Norman K. |editor-last3=Glendenning |title=Physics of Neutron Star Interiors |series=Lecture Notes in Physics |volume=578 |publisher=Springer-Verlag |year=2001 |doi=10.1007/3-540-44578-1 |isbn=978-3-540-42340-9 }}</ref>

===Stability and strange quark matter===
Ordinary quark matter consisting of up and down quarks has a very high [[Fermi energy]] compared to ordinary atomic matter and is stable only under extreme temperatures and/or pressures. This suggests that the only stable quark stars will be neutron stars with a quark matter core, while quark stars consisting entirely of ordinary quark matter will be highly unstable and re-arrange spontaneously.<ref name="Witten">{{cite journal |last1=Witten |first1=Edward |title=Cosmic separation of phases |journal=Physical Review D |volume=30 |issue=2 |pages=272–285 |date=1984 |doi=10.1103/PhysRevD.30.272 |bibcode=1984PhRvD..30..272W }}</ref><ref>{{cite journal |title=Strange matter |last1=Farhi |first1=Edward |last2=Jaffe |first2=Robert L. |journal=Physical Review D |volume=30 |issue= 11 |pages=2379 |date=1984 |bibcode=1984PhRvD..30.2379F |doi=10.1103/PhysRevD.30.2379}}</ref>

It has been shown that the high Fermi energy making ordinary quark matter unstable at low temperatures and pressures can be lowered substantially by the transformation of a sufficient number of up and down quarks into [[strange quark]]s, as strange quarks are, relatively speaking, a very heavy type of quark particle.<ref name="Witten" /> This kind of quark matter is known specifically as [[strange quark matter]] and it is speculated and subject to current scientific investigation whether it might in fact be stable under the conditions of interstellar space (i.e. near zero external pressure and temperature). If this is the case (known as the Bodmer–[[Edward Witten|Witten]] assumption), quark stars made entirely of quark matter would be stable if they quickly transform into strange quark matter.<ref name="Weber">{{Cite web|title=Strange-matter Stars |url=https://cds.cern.ch/record/278675 |last1=Weber |first1=Fridolin |last2=Kettner |first2=Christiane |last3=Weigel |first3=Manfred K. |last4=Glendenning |first4=Norman K. |journal= |date=1995 |access-date=2020-03-26 |archive-date=2022-03-22 |archive-url=https://web.archive.org/web/20220322124648/https://cds.cern.ch/record/278675 |url-status=live }} in {{cite book |title=International Symposium on Strangeness and Quark Matter, Kolymbari, Greece, 1-5 Sep 1994 |pages=308–317 |publisher=World Scientific |location=Singapore |editor-last1=Kumar |editor-first1=Shiva |editor-last2=Madsen |editor-first2=Jes |editor-last3=Panagiotou |editor-first3=Apostolos D. |editor-last4=Vassiliadis |editor-first4=G. }}</ref>

===Strange stars===
{{main|Strange star}}
Stars made of [[strange quark matter]] are known as strange stars.  These form a distinct subtype of quark stars.<ref name="Weber" />

Theoretical investigations have revealed that quark stars might not only be produced from neutron stars and powerful supernovas, they could also be created in the early [[Chronology of the universe#Hadron epoch|cosmic phase separations]] following the [[Big Bang]].<ref name="Witten" /> If these primordial quark stars transform into strange quark matter before the external temperature and pressure conditions of the early Universe makes them unstable, they might turn out stable, if the Bodmer–Witten assumption holds true. Such primordial strange stars could survive to this day.<ref name="Witten" />