Editing Supernova (section)

====Detailed process====
[[Image:Core collapse scenario.svg|upright=1.4|thumb|Within a massive, evolved star (a) the onion-layered shells of elements undergo fusion, forming an iron core (b) that reaches Chandrasekhar-mass and starts to collapse. The inner part of the core is compressed into neutrons (c), causing infalling material to bounce (d) and form an outward-propagating shock front (red). The shock starts to stall (e), but it is re-invigorated, likely by [[Supernova neutrinos|neutrino heating]]. The surrounding material is blasted away (f), leaving only a degenerate remnant.<ref name="Janka-2007"/>]]

When a stellar core is no longer supported against gravity, it collapses in on itself with velocities reaching 70,000&nbsp;km/s (0.23[[Speed of light|''c'']]),<ref name="grav_waves">
{{cite journal
 |last1=Fryer |first1=C. L.
 |last2=New |first2=K. C. B.
 |year=2003
 |title=Gravitational Waves from Gravitational Collapse
 |journal=[[Living Reviews in Relativity]]
 |volume=6 |issue=1|pages=2
 |arxiv=gr-qc/0206041
 |bibcode=2003LRR.....6....2F
 |doi=10.12942/lrr-2003-2
 |doi-access=free
 |pmc=5253977
 |pmid=28163639
}}</ref> resulting in a rapid increase in temperature and density. What follows depends on the mass and structure of the collapsing core, with low-mass degenerate cores forming neutron stars, higher-mass degenerate cores mostly collapsing completely to black holes, and non-degenerate cores undergoing runaway fusion.<ref name="Janka-2007"/><ref name="Hurley-2000">{{Cite journal |last1=Hurley |first1=J. R. |last2=Pols |first2=O. R. |last3=Tout |first3=C. A. |date=1 July 2000 |title=Comprehensive analytic formulae for stellar evolution as a function of mass and metallicity |doi-access=free |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=315 |issue=3 |pages=543–569 |doi=10.1046/j.1365-8711.2000.03426.x |bibcode=2000MNRAS.315..543H |arxiv=astro-ph/0001295 |issn=0035-8711}}</ref>

The initial collapse of degenerate cores is accelerated by [[beta decay]], photodisintegration and electron capture, which causes a burst of [[electron neutrino]]s. As the density increases, [[Supernova neutrinos|neutrino emission]] is cut off as they become trapped in the core. The inner core eventually reaches typically 30&nbsp;[[kilometre|km]] in diameter<ref name="WoosleyJanka"/> with a density comparable to that of an [[atomic nucleus]], and neutron [[degeneracy pressure]] tries to halt the collapse. If the core mass is more than about 15 solar masses then neutron degeneracy is insufficient to stop the collapse and a black hole forms directly with no supernova.<ref name=renzon2018/>

In lower mass cores the collapse is stopped and the newly formed neutron core has an initial temperature of about 100&nbsp;billion [[kelvin]], 6,000 times the temperature of the [[Sun's core]].<ref name="Janka-2007">
{{Cite journal
 |last1=Janka |first1=H.-T.
 |last2=Langanke |first2=K.
 |last3=Marek |first3=A.
 |last4=Martínez-Pinedo |first4=G.
 |last5=Müller |first5=B.
 |title=Theory of core-collapse supernovae
 |journal=[[Physics Reports]]
 |volume=442 |issue=1–6
 |pages=38–74 |year=2007
 |arxiv=astro-ph/0612072
 |bibcode=2007PhR...442...38J
 |doi=10.1016/j.physrep.2007.02.002
|s2cid=15819376
 }}</ref> At this temperature, neutrino-antineutrino pairs of all [[Neutrino oscillation|flavours]] are efficiently formed by [[Thermal radiation|thermal emission]]. These thermal neutrinos are several times more abundant than the electron-capture neutrinos.<ref>
{{Cite book
 |last1=Gribbin |first1=J. R.
 |last2=Gribbin |first2=M.
 |date=2000
 |title=Stardust: Supernovae and Life – The Cosmic Connection
 |publisher=[[Yale University Press]]
 |page=173
 |isbn=978-0-300-09097-0
 |bibcode=2000sslc.book.....G
}}</ref> About 10<sup>46</sup> joules, approximately 10% of the star's rest mass, is converted into a ten-second burst of neutrinos, which is the main output of the event.<ref name="WoosleyJanka"/><ref name="barwick">
{{Cite arXiv
 |last1=Barwick |first1=S. W
 |last2=Beacom |first2=J. F
 |last3=Cianciolo |first3=V.
 |last4=Dodelson |first4=S.
 |last5=Feng |first5=J. L
 |last6=Fuller |first6=G. M
 |last7=Kaplinghat |first7=M.
 |last8=McKay |first8=D. W
 |last9=Meszaros |first9=P.
 |last10=Mezzacappa |first10=A.
 |last11=Murayama |first11=H.
 |last12=Olive |first12=K. A
 |last13=Stanev |first13=T.
 |last14=Walker |first14=T. P
 |year=2004
 |title=APS Neutrino Study: Report of the Neutrino Astrophysics and Cosmology Working Group
 |eprint=astro-ph/0412544
}}</ref> The suddenly halted core collapse rebounds and produces a shock wave that stalls in the outer core within milliseconds<ref>
{{Cite journal
 |last1=Myra |first1=E. S.
 |last2=Burrows |first2=A.
 |date=1990
 |title=Neutrinos from type II supernovae- The first 100 milliseconds
 |journal=[[Astrophysical Journal]]
 |volume=364 |pages=222–231
 |bibcode=1990ApJ...364..222M
 |doi=10.1086/169405
|doi-access=free
 }}</ref> as energy is lost through the dissociation of heavy elements. A process that is {{As of|2023|alt=not clearly understood}} is necessary to allow the outer layers of the core to reabsorb around 10<sup>44</sup> joules<ref name="barwick"/> (1 [[Foe (unit)|foe]]) from the [[Supernova neutrinos|neutrino pulse]], producing the visible brightness, although there are other theories that could power the explosion.<ref name="WoosleyJanka"/>

Some material from the outer envelope falls back onto the neutron star, and, for cores beyond about {{Solar mass|8}}, there is sufficient fallback to form a black hole. This fallback will reduce the kinetic energy created and the mass of expelled radioactive material, but in some situations, it may also generate [[relativistic jet]]s that result in a [[gamma-ray burst]] or an exceptionally luminous supernova.<ref name=piram2019>{{cite journal |bibcode=2019ApJ...871L..25P |title=Relativistic Jets in Core-collapse Supernovae |last1=Piran |first1=Tsvi |last2=Nakar |first2=Ehud |last3=Mazzali |first3=Paolo |last4=Pian |first4=Elena |journal=The Astrophysical Journal |year=2019 |volume=871 |issue=2 |pages=L25 |doi=10.3847/2041-8213/aaffce |s2cid=19266567 |doi-access=free |arxiv=1704.08298 }}</ref>

The collapse of a massive non-degenerate core will ignite further fusion.<ref name="Hurley-2000"/> When the core collapse is initiated by [[Pair-instability supernova|pair instability]] ([[photon]]s turning into [[electron]]-[[positron]] pairs, thereby reducing the radiation pressure) oxygen fusion begins and the collapse may be halted. For core masses of {{Solar mass|40–60}}, the collapse halts and the star remains intact, but collapse will occur again when a larger core has formed. For cores of around {{Solar mass|60–130}}, the fusion of oxygen and heavier elements is so energetic that the entire star is disrupted, causing a supernova. At the upper end of the mass range, the supernova is unusually luminous and extremely long-lived due to many solar masses of ejected <sup>56</sup>Ni. For even larger core masses, the core temperature becomes high enough to allow photodisintegration and the core collapses completely into a black hole.<ref name="kasen">
{{Cite journal
 |last1=Kasen |first1=D.
 |last2=Woosley |first2=S. E.
 |last3=Heger |first3=A.
 |year=2011
 |title=Pair Instability Supernovae: Light Curves, Spectra, and Shock Breakout
 |journal=[[The Astrophysical Journal]]
 |volume=734 |issue=2 |pages=102
 |arxiv=1101.3336
 |bibcode=2011ApJ...734..102K
 |doi=10.1088/0004-637X/734/2/102
|s2cid=118508934
 }}</ref><ref name=renzon2018/>