Editing Chandrasekhar limit (section)

==Applications==
The core of a star is kept from collapsing by the heat generated by the [[nuclear fusion|fusion]] of [[Atomic nucleus|nuclei]] of lighter [[chemical element|elements]] into heavier ones. At various stages of [[stellar evolution]], the nuclei required for this process are exhausted, and the core collapses, causing it to become denser and hotter. A critical situation arises when [[iron]] accumulates in the core, since iron nuclei are incapable of generating further energy through fusion. If the core becomes sufficiently dense, electron degeneracy pressure will play a significant part in stabilizing it against gravitational collapse.<ref name="evo2">{{cite journal | last1 = Woosley | first1 = S. E. | last2 = Heger | first2 = A. | last3 = Weaver | first3 = T. A. | s2cid = 55932331 | year = 2002 | title = The evolution and explosion of massive stars | journal = Reviews of Modern Physics | volume = 74 | issue = 4| pages = 1015–1071 | bibcode=2002RvMP...74.1015W | doi=10.1103/revmodphys.74.1015}}</ref>

If a main-sequence star is not too massive (less than approximately 8 [[solar mass]]es), it eventually sheds enough mass to form a white dwarf having mass below the Chandrasekhar limit, which consists of the former core of the star. For more-massive stars, electron degeneracy pressure does not keep the iron core from collapsing to very great density, leading to formation of a [[neutron star]], [[black hole]], or, speculatively, a [[quark star]].  (For very massive, low-[[metallicity]] stars, it is also possible that instabilities destroy the star completely.)<ref name="ifmr1">{{cite journal | last1 = Koester | first1 = D. | last2 = Reimers | first2 = D. | year = 1996 | title = White dwarfs in open clusters. VIII. NGC 2516: a test for the mass-radius and initial-final mass relations | journal = Astronomy and Astrophysics | volume = 313 | pages = 810–814 | bibcode=1996A&A...313..810K}}</ref><ref name="ifmr2">Kurtis A. Williams, M. Bolte, and Detlev Koester 2004 [http://adsabs.harvard.edu/abs/2004ApJ...615L..49W An Empirical Initial-Final Mass Relation from Hot, Massive White Dwarfs in NGC 2168 (M35)] {{Webarchive|url=https://web.archive.org/web/20070819215754/http://adsabs.harvard.edu/abs/2004ApJ...615L..49W |date=2007-08-19 }},  ''Astrophysical Journal'' '''615''', pp. L49–L52 [https://arxiv.org/abs/astro-ph/0409447 arXiv astro-ph/0409447] {{Webarchive|url=https://web.archive.org/web/20070819215754/http://adsabs.harvard.edu/abs/2004ApJ...615L..49W |date=2007-08-19 }}.</ref><ref name="evo">{{cite journal | last1 = Heger | first1 = A. | last2 = Fryer | first2 = C. L. | last3 = Woosley | first3 = S. E. | last4 = Langer | first4 = N. | last5 = Hartmann | first5 = D. H. | year = 2003 | title = How Massive Single Stars End Their Life | journal = Astrophysical Journal | volume = 591 | issue = 1| pages = 288–300 | bibcode=2003ApJ...591..288H | doi=10.1086/375341|arxiv = astro-ph/0212469 | s2cid = 59065632 }}</ref><ref>{{cite journal | last1 = Schaffner-Bielich | first1 = Jürgen | year = 2005 | title = Strange quark matter in stars: a general overview] | arxiv = astro-ph/0412215 | journal = Journal of Physics G: Nuclear and Particle Physics | volume = 31 | issue = 6| pages = S651–S657 | doi=10.1088/0954-3899/31/6/004|bibcode = 2005JPhG...31S.651S | s2cid = 118886040 }}</ref> During the collapse, [[neutron]]s are formed by the capture of [[electron]]s by [[proton]]s in the process of [[electron capture]], leading to the emission of [[neutrino]]s.<ref name="evo2" />{{rp|pp=1046–1047}} The decrease in [[gravitational energy|gravitational potential energy]] of the collapsing core releases a large amount of energy on the order of {{val|e=46|ul=J}} (100&nbsp;[[foe (unit)|foe]]s). Most of this energy is carried away by the emitted neutrinos<ref name="physns">{{cite journal |last1=Lattimer |first1=James M. |last2=Prakash |first2=Madappa |year=2004 |title=The Physics of Neutron Stars |arxiv=astro-ph/0405262 |journal=Science |volume=304 |issue=5670 |pages=536–542 |doi=10.1126/science.1090720 |pmid=15105490 |bibcode=2004Sci...304..536L |s2cid=10769030 }}</ref> and the kinetic energy of the expanding shell of gas; only about 1% is emitted as optical light.<ref>Schneider, Stephen E.; and Arny, Thomas T.; [http://abyss.uoregon.edu/~js/ast122/lectures/lec18.html ''Readings: Unit 66: End of a star's life''] {{Webarchive|url=https://web.archive.org/web/20200214212338/http://abyss.uoregon.edu/~js/ast122/lectures/lec18.html |date=2020-02-14 }}, Astronomy 122: ''Birth and Death of Stars'', University of Oregon</ref> This process is believed responsible for [[core-collapse supernova|supernovae of types Ib, Ic, and II]].<ref name="evo2" />

[[Type Ia supernova]]e derive their energy from runaway fusion of the nuclei in the interior of a [[white dwarf]]. This fate may befall [[carbon]]–[[oxygen]] white dwarfs that accrete matter from a companion [[giant star]], leading to a steadily increasing mass. As the white dwarf's mass approaches the Chandrasekhar limit, its central density increases, and, as a result of [[compression (physical)|compression]]al heating, its temperature also increases. This eventually ignites [[nuclear fusion]] reactions, leading to an immediate [[carbon detonation]], which disrupts the star and causes the supernova.<ref name="sniamodels">{{cite journal |last1=Hillebrandt |first1=Wolfgang |last2=Niemeyer |first2=Jens C. |year=2000 |title=Type IA Supernova Explosion Models |journal=Annual Review of Astronomy and Astrophysics |volume=38 |pages=191–230 |doi=10.1146/annurev.astro.38.1.191 |bibcode=2000ARA&A..38..191H |arxiv = astro-ph/0006305 |s2cid=10210550 }}</ref>{{rp|loc=§5.1.2}}

A strong indication of the reliability of Chandrasekhar's formula is that the [[absolute magnitude]]s of supernovae of Type Ia are all approximately the same; at maximum luminosity, {{math|''M''<sub>V</sub>}} is approximately −19.3, with a [[standard deviation]] of no more than 0.3.<ref name="sniamodels"/>{{rp|loc=eq. (1)}}  A [[Confidence interval|1-sigma interval]] therefore represents a factor of less than 2 in luminosity. This seems to indicate that all type Ia supernovae convert approximately the same amount of mass to energy.