Editing Supernova (section)

==Current models==
[[File:The Rise and Fall of a Supernova.jpg|thumb|upright=1.7|In the galaxy [[NGC 1365]] a supernova (the bright dot slightly above the galactic center) rapidly brightens, then fades more slowly.<ref>
{{cite news
 |title=The Rise and Fall of a Supernova
 |url=http://www.eso.org/public/images/potw1323a/
 |newspaper=ESO Picture of the Week
 |access-date=14 June 2013
|url-status=live
 |archive-url=https://web.archive.org/web/20130702042133/http://www.eso.org/public/images/potw1323a/
 |archive-date=2 July 2013
}}</ref>]]

Supernova type codes, as summarised in the table above, are ''[[Taxonomy (general)|taxonomic]]'': the type number is based on the light observed from the supernova, not necessarily its cause. For example, type Ia supernovae are produced by runaway fusion ignited on degenerate white dwarf progenitors, while the spectrally similar type Ib/c are produced from massive stripped progenitor stars by core collapse.

===Thermal runaway===
{{Main|Type Ia supernova}}
[[File:Progenitor IA supernova.svg|thumb|upright=1.7|Formation of a type Ia supernova]]
A white dwarf star may accumulate sufficient material from a stellar companion to raise its core temperature enough to [[Carbon detonation|ignite]] [[Carbon burning process|carbon fusion]], at which point it undergoes [[Thermal runaway|runaway]] nuclear fusion, completely disrupting it. There are three avenues by which this detonation is theorised to happen: stable [[accretion (astrophysics)|accretion]] of material from a companion, the collision of two white dwarfs, or accretion that causes ignition in a shell that then ignites the core. The dominant mechanism by which type Ia supernovae are produced remains unclear.<ref name="Piro2014">
{{Cite journal
 |last1=Piro |first1=A. L.
 |last2=Thompson |first2=T. A.
 |last3=Kochanek |first3=C. S.
 |year=2014
 |title=Reconciling 56Ni production in Type Ia supernovae with double degenerate scenarios
 |journal=[[Monthly Notices of the Royal Astronomical Society]]
 |volume=438 |issue=4 |pages=3456
 |arxiv=1308.0334
 |bibcode=2014MNRAS.438.3456P
 |doi=10.1093/mnras/stt2451
|doi-access=free
 |s2cid=27316605
 }}</ref> Despite this uncertainty in how type Ia supernovae are produced, type Ia supernovae have very uniform properties and are useful [[Cosmic distance ladder|standard candles]] over intergalactic distances. Some calibrations are required to compensate for the gradual change in properties or different frequencies of abnormal luminosity supernovae at high redshift, and for small variations in brightness identified by light curve shape or spectrum.<ref name="chen">
{{Cite journal
 |last1=Chen |first1=W.-C.
 |last2=Li |first2=X.-D.
 |year=2009
 |title=On the Progenitors of Super-Chandrasekhar Mass Type Ia Supernovae
 |journal=[[The Astrophysical Journal]]
 |volume=702 |issue=1|pages=686–691
 |arxiv=0907.0057
 |bibcode=2009ApJ...702..686C
 |doi=10.1088/0004-637X/702/1/686
|s2cid=14301164
 }}</ref><ref>
{{Cite journal
 |last1=Howell |first1=D. A.
 |last2=Sullivan |first2=M.
 |last3=Conley |first3=A. J.
 |last4=Carlberg |first4=R. G.
 |date=2007
 |title=Predicted and Observed Evolution in the Mean Properties of Type Ia Supernovae with Redshift
 |journal=[[Astrophysical Journal Letters]]
 |volume=667 |issue=1 |pages=L37–L40
 |arxiv=astro-ph/0701912
 |bibcode=2007ApJ...667L..37H
 |doi=10.1086/522030
|s2cid=16667595
 }}</ref>

====Normal type Ia====
There are several means by which a supernova of this type can form, but they share a common underlying mechanism. If a [[carbon]]-[[oxygen]] white dwarf accreted enough matter to reach the [[Chandrasekhar limit]] of about 1.44 [[solar mass]]es<ref name="Mazzali2007">
{{Cite journal
 |last1=Mazzali |first1=P. A.
 |last2=Röpke |first2=F. K.
 |last3=Benetti |first3=S.
 |last4=Hillebrandt |first4=W.
 |date=2007
 |title=A Common Explosion Mechanism for Type Ia Supernovae
 |journal=[[Science (journal)|Science]]
 |volume=315 |issue=5813 |pages=825–828
 |arxiv=astro-ph/0702351
 |bibcode=2007Sci...315..825M
 |doi=10.1126/science.1136259
 |pmid=17289993
|s2cid=16408991
 }}</ref> (for a non-rotating star), it would no longer be able to support the bulk of its mass through [[electron degeneracy pressure]]<ref name="Chandrasekhar">{{Cite journal
 |last1=Lieb
 |first1=E. H.
 |last2=Yau
 |first2=H.-T.
 |date=1987
 |title=A rigorous examination of the Chandrasekhar theory of stellar collapse
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 |volume=323
 |issue=1
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|archive-date=3 March 2020
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 }}</ref><ref name=canal1997>
{{Cite book
 |last1=Canal |first1=R.
 |last2=Gutiérrez |first2=J. L.
 |date=1997
 |chapter=The possible white dwarf-neutron star connection
 |editor1-last=Isern |editor1-first=J.
 |editor2-last=Hernanz |editor2-first=M.
 |editor3-last=Gracia-Berro |editor3-first=E.
 |title=White Dwarfs: Proceedings of the 10th European Workshop on White Dwarfs
 |series=Astrophysics and Space Science Library
 |volume=214 |page=49
 |publisher=[[Kluwer Academic Publishers]]
 |location=Dordrecht
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 |bibcode=1997ASSL..214...49C
 |doi=10.1007/978-94-011-5542-7_7
 |isbn=978-0-7923-4585-5
|s2cid=9288287
 }}</ref> and would begin to collapse. However, the current view is that this limit is not normally attained; increasing temperature and density inside the core ignite carbon fusion as the star approaches the limit (to within about 1%)<ref>
{{Cite book
 |last=Wheeler |first=J. C.
 |date=2000
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 |archive-date=10 September 2015
}}</ref> before collapse is initiated.<ref name="Mazzali2007"/> In contrast, for a core primarily composed of oxygen, neon and magnesium, the collapsing white dwarf will typically form a [[neutron star]]. In this case, only a fraction of the star's mass will be ejected during the collapse.<ref name=canal1997/>

[[File:An isolated neutron star in the Small Magellanic Cloud.jpg|thumb|The blue spot at the centre of the red ring is an isolated neutron star in the [[Small Magellanic Cloud]].]]
Within a few seconds of the collapse process, a substantial fraction of the matter in the white dwarf undergoes nuclear fusion, releasing enough energy (1–{{val|2|e=44|ul=J}})<ref name="aaa270">
{{Cite journal
 |last1=Khokhlov |first1=A. M.
 |last2=Mueller |first2=E.
 |last3=Höflich |first3=P. A.
 |date=1993
 |title=Light curves of Type IA supernova models with different explosion mechanisms
 |journal=[[Astronomy and Astrophysics]]
 |volume=270 |issue=1–2 |pages=223–248
 |bibcode=1993A&A...270..223K
}}</ref> to [[gravitational binding energy|unbind]] the star in a supernova.<ref name="ropke">
{{Cite journal
 |last1=Röpke |first1=F. K.
 |last2=Hillebrandt |first2=W.
 |date=2004
 |title=The case against the progenitor's carbon-to-oxygen ratio as a source of peak luminosity variations in type Ia supernovae
 |journal=[[Astronomy and Astrophysics Letters]]
 |volume=420 |issue=1 |pages=L1–L4
 |arxiv=astro-ph/0403509
 |bibcode=2004A&A...420L...1R
 |doi=10.1051/0004-6361:20040135
|s2cid=2849060
 }}</ref> An outwardly expanding [[shock wave]] is generated, with matter reaching velocities on the order of 5,000–20,000 [[kilometers per second|km/s]], or roughly 3% of the speed of light. There is also a significant increase in luminosity, reaching an [[absolute magnitude]] of −19.3 (or 5&nbsp;billion times brighter than the Sun), with little variation.<ref name="explosion_model">
{{Cite journal
 |last1=Hillebrandt |first1=W.
 |last2=Niemeyer |first2=J. C.
 |date=2000
 |title=Type IA Supernova Explosion Models
 |journal=[[Annual Review of Astronomy and Astrophysics]]
 |volume=38 |issue=1 |pages=191–230
 |arxiv=astro-ph/0006305
 |bibcode=2000ARA&A..38..191H
 |doi=10.1146/annurev.astro.38.1.191
|s2cid=10210550
 }}</ref>

The model for the formation of this category of supernova is a close binary star system. The larger of the two stars is the first to [[Stellar evolution|evolve]] off the [[main sequence]], and it expands to form a [[red giant]]. The two stars now share a common envelope, causing their mutual orbit to shrink. The giant star then sheds most of its envelope, losing mass until it can no longer continue [[nuclear fusion]]. At this point, it becomes a white dwarf star, composed primarily of carbon and oxygen.<ref>
{{cite conference
 |last=Paczyński |first=B.
 |date=1976
 |title=Common Envelope Binaries
 |book-title=Structure and Evolution of Close Binary Systems
 |conference=IAU Symposium No. 73
 |editor1-last=Eggleton |editor1-first=P.
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}}</ref> Eventually, the secondary star also evolves off the main sequence to form a red giant. Matter from the giant is accreted by the white dwarf, causing the latter to increase in mass. The exact details of initiation and of the heavy elements produced in the catastrophic event remain unclear.<ref>{{Cite journal |last1=Poludnenko |first1=Alexei Y. |last2=Chambers |first2=Jessica |last3=Ahmed |first3=Kareem |last4=Gamezo |first4=Vadim N. |last5=Taylor |first5=Brian D. |date=November 2019 |title=A unified mechanism for unconfined deflagration-to-detonation transition in terrestrial chemical systems and type Ia supernovae |url=https://www.science.org/doi/10.1126/science.aau7365 |journal=Science |language=en |volume=366 |issue=6465 |pages=eaau7365 |bibcode=2019Sci...366.7365P |doi=10.1126/science.aau7365 |pmid=31672866 |arxiv=1911.00050 |s2cid=207817150 |issn=0036-8075 |quote=Theoretical models of SNIa have remained limited because of uncertainties in the explosion mechanisms. [...] SNIa explosions are driven by fast thermonuclear burning in <sup>12</sup>C/<sup>16</sup>O white dwarf (WD) stars with a mass close to, or below, the Chandrasekhar mass limit of ≈1.4 solar masses [...] Beyond this general statement, however, the exact mechanisms of SNIa remain unclear, with a number of possible scenarios.}}</ref>

Type Ia supernovae produce a characteristic light curve—the graph of luminosity as a function of time—after the event. This luminosity is generated by the [[radioactive decay]] of [[nickel]]-56 through [[cobalt]]-56 to [[iron]]-56.<ref name="explosion_model"/> The peak luminosity of the light curve is extremely consistent across normal type Ia supernovae, having a maximum absolute magnitude of about −19.3. This is because typical type Ia supernovae arise from a consistent type of progenitor star by gradual mass acquisition, and explode when they acquire a consistent typical mass, giving rise to very similar supernova conditions and behaviour. This allows them to be used as a secondary<ref>
{{Cite journal
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A second model for the formation of type Ia supernovae involves the merger of two white dwarf stars, with the combined mass momentarily exceeding the Chandrasekhar limit.<ref>
{{cite journal
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 |last2=Blinnikov |first2=S.
 |last3=Canal |first3=R.
 |last4=Mendez |first4=J.
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 |last6=Visco |first6=A.
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 |year=2000
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 |volume=71 |pages=435
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}}</ref> This is sometimes referred to as the double-degenerate model, as both stars are degenerate white dwarfs. Due to the possible combinations of mass and chemical composition of the pair there is much variation in this type of event,<ref>
{{cite journal
 |last1=Dan |first1=M.
 |last2=Rosswog |first2=S.
 |last3=Guillochon |first3=J.
 |last4=Ramirez-Ruiz |first4=E.
 |year=2012
 |title=How the merger of two white dwarfs depends on their mass ratio: Orbital stability and detonations at contact
 |journal=[[Monthly Notices of the Royal Astronomical Society]]
 |volume=422|issue=3|pages=2417
 |arxiv=1201.2406
 |bibcode=2012MNRAS.422.2417D
 |doi=10.1111/j.1365-2966.2012.20794.x
 |doi-access=free
 | s2cid=119159904
}}</ref> and, in many cases, there may be no supernova at all, in which case they will have a less luminous light curve than the more normal SN type Ia.<ref>{{Cite journal |last1=Maoz |first1=Dan |last2=Mannucci |first2=Filippo |last3=Nelemans |first3=Gijs |date=18 August 2014 |title=Observational Clues to the Progenitors of Type Ia Supernovae |url=https://www.annualreviews.org/doi/10.1146/annurev-astro-082812-141031 |journal=Annual Review of Astronomy and Astrophysics |language=en |volume=52 |issue=1 |pages=107–170 |doi=10.1146/annurev-astro-082812-141031 |bibcode=2014ARA&A..52..107M |arxiv=1312.0628 |s2cid=55533680 |issn=0066-4146}}</ref>

====Non-standard type Ia====
Abnormally bright type Ia supernovae occur when the white dwarf already has a mass higher than the Chandrasekhar limit,<ref>
{{Cite journal
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 |last17=Pritchet |first17=C. J.
 |year=2006
 |title=The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-mass white dwarf star
 |journal=[[Nature (journal)|Nature]]
 |volume=443 |issue=7109 |pages=308–311
 |arxiv=astro-ph/0609616
 |bibcode=2006Natur.443..308H
 |doi=10.1038/nature05103
 |pmid=16988705
|s2cid=4419069
 }}</ref> possibly enhanced further by asymmetry,<ref>
{{Cite journal
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 |last7=Nomoto |first7=K. I.
 |last8=Iye |first8=M.
 |last9=Sasaki |first9=T.
 |last10=Mazzali |first10=P. A.
 |last11=Pian |first11=E.
 |year=2010
 |title=Spectropolarimetry of Extremely Luminous Type Ia Supernova 2009dc: Nearly Spherical Explosion of Super-Chandrasekhar Mass White Dwarf
 |journal=[[The Astrophysical Journal]]
 |volume=714 |issue=2 |pages=1209
 |arxiv=0908.2057
 |bibcode=2010ApJ...714.1209T
 |doi=10.1088/0004-637X/714/2/1209
|s2cid=13990681
 }}</ref> but the ejected material will have less than normal kinetic energy. This super-Chandrasekhar-mass scenario can occur, for example, when the extra mass is supported by [[differential rotation]].<ref>{{cite journal | title=Thermonuclear explosions of rapidly differentially rotating white dwarfs: Candidates for superluminous Type Ia supernovae? | last1=Fink | first1=M. | last2=Kromer | first2=M. | last3=Hillebrandt | first3=W. | last4=Röpke | first4=F. K. | last5=Pakmor | first5=R. | last6=Seitenzahl | first6=I. R. | last7=Sim | first7=S. A. | journal=Astronomy & Astrophysics | volume=618 | id=A124 | date=October 2018 | pages=A124 | doi=10.1051/0004-6361/201833475 | arxiv=1807.10199 | bibcode=2018A&A...618A.124F | s2cid=118965737 }}</ref>

There is no formal sub-classification for non-standard type Ia supernovae. It has been proposed that a group of sub-luminous supernovae that occur when helium accretes onto a white dwarf should be classified as '''type Iax'''.<ref name=wang>
{{cite journal
 |last1=Wang |first1=B.
 |last2=Liu |first2=D.
 |last3=Jia |first3=S.
 |last4=Han |first4=Z.
 |year=2014
 |title=Helium double-detonation explosions for the progenitors of type Ia supernovae
 |journal=[[Proceedings of the International Astronomical Union]]
 |volume=9 |issue=S298 |pages=442
 |arxiv=1301.1047
 |bibcode=2014IAUS..298..442W
 |doi=10.1017/S1743921313007072
|s2cid=118612081
 }}</ref><ref name=foley>
{{cite journal
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 |last3=Chornock |first3=R.
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 |last6=Marion |first6=G. H.
 |last7=Morrell |first7=N. I.
 |last8=Pignata |first8=G.
 |last9=Stritzinger |first9=M. D.
 |last10=Silverman |first10=J. M.
 |last11=Wang |first11=X.
 |last12=Anderson |first12=J. P.
 |last13=Filippenko |first13=A. V.
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 |arxiv=1212.2209
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 |doi=10.1088/0004-637X/767/1/57
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 }}</ref> This type of supernova may not always completely destroy the white dwarf progenitor and could leave behind a [[zombie star]].<ref name="mccully">
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 |arxiv=1408.1089
 |bibcode=2014Natur.512...54M
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|s2cid=4464556
 }}</ref>

One specific type of supernova originates from exploding white dwarfs, like type Ia, but contains hydrogen lines in their spectra, possibly because the white dwarf is surrounded by an envelope of hydrogen-rich [[Circumstellar disc|circumstellar material]]. These supernovae have been dubbed '''type Ia/IIn''', '''type Ian''', '''type IIa''' and '''type IIan'''.<ref>
{{cite journal
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 |last16=Graham |first16=M. L.
 |last17=Griffith |first17=C. V.
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 |last19=Kasliwal |first19=M. M.
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 |last27=Pan |first27=Y.-C.
 |last28=Perley |first28=D. A.
 |last29=Poznanski |first29=D.
 |last30=Quimby |first30=R. M.
 |year=2013
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 |volume=207 |issue=1 |pages=3
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|s2cid=51415846
 }}</ref>

The quadruple star [[HD 74438]], belonging to the open cluster [[IC 2391]] the [[Vela constellation]], has been predicted to become a non-standard type Ia supernova.<ref name="GIAISURVEY">{{cite journal |last1=Gilmore |first1=Gerry |last2=Randich |first2=Sofia |title=The Gaia-ESO Public Spectroscopic Survey |journal=The Messenger |date=March 2012 |volume=147 |issue=147 |pages=25–31 |publisher=European Southern Observatory |location=Garching, Germany |language=en |bibcode=2012Msngr.147...25G}}</ref><ref name="supernova">{{cite journal |last1=Merle |first1=Thibault |last2=Hamers |first2=Adrian S. |last3=Van Eck |first3=Sophie |last4=Jorissen |first4=Alain |last5=Van der Swaelmen |first5=Mathieu |last6=Pollard |first6=Karen |last7=Smiljanic |first7=Rodolfo |last8=Pourbaix |first8=Dimitri |last9=Zwitter |first9=Tomaž |last10=Traven |first10=Gregor |last11=Gilmore |first11=Gerry |last12=Randich |first12=Sofia |last13=Gonneau |first13=Anaïs |last14=Hourihane |first14=Anna |last15=Sacco |first15=Germano |last16=Worley |first16=C. Clare |title=A spectroscopic quadruple as a possible progenitor of sub-Chandrasekhar type Ia supernovae |journal=Nature Astronomy |date=12 May 2022 |volume=6 |issue=6 |pages=681–688 |doi=10.1038/s41550-022-01664-5|arxiv=2205.05045 |bibcode=2022NatAs...6..681M |s2cid=248665714 }}</ref>

===Core collapse===
[[Image:Evolved star fusion shells.svg|thumb|The layers of a massive, evolved star just before core collapse (not to scale)]]
Very massive stars can undergo core collapse when nuclear fusion becomes unable to sustain the core against its own gravity; passing this threshold is the cause of all types of supernova except type Ia. The collapse may cause violent expulsion of the outer layers of the star resulting in a supernova. However, if the release of gravitational potential energy is insufficient, the star may instead collapse into a [[black hole]] or neutron star with little radiated energy.<ref name="heger"/>

Core collapse can be caused by several different mechanisms: exceeding the [[Chandrasekhar limit]]; [[electron capture]]; [[Pair-instability supernova|pair-instability]]; or [[photodisintegration]].<ref name="heger">
{{Cite journal
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 |arxiv=astro-ph/0212469
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 }}</ref><ref name=renzon2018>{{cite journal |bibcode=2020A&A...640A..56R |title=Predictions for the hydrogen-free ejecta of pulsational pair-instability supernovae |last1=Renzo |first1=M. |last2=Farmer |first2=R. |last3=Justham |first3=S. |last4=Götberg |first4=Y. |last5=De Mink |first5=S. E. |last6=Zapartas |first6=E. |last7=Marchant |first7=P. |last8=Smith |first8=N. |journal=Astronomy and Astrophysics |year=2020 |volume=640 |pages=A56 |doi=10.1051/0004-6361/202037710 |arxiv=2002.05077 |s2cid=211082844 }}</ref><ref name="nomoto">
{{Cite journal
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* When a massive star develops an iron core larger than the Chandrasekhar mass it will no longer be able to support itself by [[electron degeneracy pressure]] and will collapse further to a neutron star or black hole.
* Electron capture by magnesium in a [[degenerate matter|degenerate]] O/Ne/Mg core (8–10 solar mass progenitor star) removes support and causes [[gravitational collapse]] followed by explosive oxygen fusion, with very similar results.
* Electron-positron pair production in a large post-helium burning core removes thermodynamic support and causes initial collapse followed by runaway fusion, resulting in a pair-instability supernova.
* A sufficiently large and hot [[stellar core]] may generate gamma-rays energetic enough to initiate photodisintegration directly, which will cause a complete collapse of the core.

The table below lists the known reasons for core collapse in massive stars, the types of stars in which they occur, their associated supernova type, and the remnant produced. The [[metallicity]] is the proportion of elements other than hydrogen or helium, as compared to the Sun. The initial mass is the mass of the star prior to the supernova event, given in multiples of the Sun's mass, although the mass at the time of the supernova may be much lower.<ref name="heger"/>

Type IIn supernovae are not listed in the table. They can be produced by various types of core collapse in different progenitor stars, possibly even by type Ia white dwarf ignitions, although it seems that most will be from iron core collapse in luminous [[supergiant]]s or [[hypergiant]]s (including LBVs). The narrow spectral lines for which they are named occur because the supernova is expanding into a small dense cloud of circumstellar material.<ref name="moriya">
{{cite journal
 |last1=Moriya |first1=T. J.
 |date=2012
 |title=Progenitors of Recombining Supernova Remnants
 |journal=[[The Astrophysical Journal]]
 |volume=750 |issue=1 |pages=L13
 |arxiv=1203.5799
 |bibcode=2012ApJ...750L..13M
 |doi=10.1088/2041-8205/750/1/L13
|s2cid=119209527
 }}</ref> It appears that a significant proportion of supposed type IIn supernovae are supernova impostors, massive eruptions of LBV-like stars similar to the Great Eruption of [[Eta Carinae]]. In these events, material previously ejected from the star creates the narrow absorption lines and causes a shock wave through interaction with the newly ejected material.<ref name="smith">
{{Cite journal
 |last1=Smith |first1=N.
 |last2=Ganeshalingam |first2=M.
 |last3=Chornock |first3=R.
 |last4=Filippenko |first4=A. V.
 |last5=Li |first5=W.
 |last6=Silverman |first6=J. M.
 |last7=Steele |first7=T. N.
 |last8=Griffith |first8=C. V.
 |last9=Joubert |first9=N.
 |last10=Lee |first10=N. Y.
 |last11=Lowe |first11=T. B.
 |last12=Mobberley |first12=M. P.
 |last13=Winslow |first13=D. M.
 |year=2009
 |title=Sn 2008S: A Cool Super-Eddington Wind in a Supernova Impostor
 |journal=[[The Astrophysical Journal]]
 |volume=697 |issue=1|pages=L49
 |arxiv=0811.3929
 |bibcode=2009ApJ...697L..49S
 |doi=10.1088/0004-637X/697/1/L49
|s2cid=17627678
 }}</ref>

{|class="wikitable"
|+ Core collapse scenarios by mass and metallicity<ref name="heger"/>
|-
! Cause of collapse !! Progenitor star approximate initial mass ([[solar mass]]es) !! Supernova type !! Remnant
|-
| [[Electron capture supernova|Electron capture in a degenerate O+Ne+Mg core]] || 9–10 || Faint II-P ||Neutron star
|-
|rowspan="7"| Iron core collapse || 10–25 || Faint II-P || Neutron star
|-
| 25–40 with low or solar metallicity || Normal II-P || Black hole after fallback of material onto an initial neutron star
|-
| 25–40 with very high metallicity || II-L or II-b || Neutron star
|-
| 40–90 with low metallicity || None || Black hole
|-
| ≥&nbsp;40 with near-solar metallicity || Faint Ib/c, or [[hypernova]] with [[gamma-ray burst]] (GRB) || Black hole after fallback of material onto an initial neutron star
|-
| ≥&nbsp;40 with very high metallicity || Ib/c || Neutron star
|-
| ≥&nbsp;90 with low metallicity || None, possible GRB || Black hole
|-
| Pair instability{{anchor|type_II_P_anchor}} || 140–250 with low metallicity || II-P, sometimes a hypernova, possible GRB || No remnant
|-
| Photodisintegration || ≥&nbsp;250 with low metallicity || None (or luminous supernova?), possible GRB || Massive black hole
|}

====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
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}}</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.
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|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.
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 |date=2000
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 |page=173
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}}</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
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 |last2=Beacom |first2=J. F
 |last3=Cianciolo |first3=V.
 |last4=Dodelson |first4=S.
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 |last6=Fuller |first6=G. M
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 |last11=Murayama |first11=H.
 |last12=Olive |first12=K. A
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 |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.
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|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
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 |bibcode=2011ApJ...734..102K
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|s2cid=118508934
 }}</ref><ref name=renzon2018/>

====Type II====
{{Main|Type II supernova}}
[[Image:SN 1997D.jpg|thumb|The atypical subluminous type II [[SN 1997D]]]]
Stars with initial masses less than about {{Solar mass|8}} never develop a core large enough to collapse and they eventually lose their atmospheres to become white dwarfs. Stars with at least {{Solar mass|9}} (possibly as much as {{Solar mass|12}}<ref name="superagb">
{{Cite journal
 |last1=Poelarends |first1=A. J. T.
 |last2=Herwig |first2=F.
 |last3=Langer |first3=N.
 |last4=Heger |first4=A.
 |year=2008
 |title=The Supernova Channel of Super-AGB Stars
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 |volume=675 |issue=1|pages=614–625
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|s2cid=18334243
 }}</ref>) evolve in a complex fashion, progressively burning heavier elements at hotter temperatures in their cores.<ref name="WoosleyJanka">
{{Cite journal
 |last1=Woosley |first1=S. E.
 |last2=Janka |first2=H.-T.
 |date=2005
 |title=The Physics of Core-Collapse Supernovae
 |journal=[[Nature Physics]]
 |volume=1 |issue=3 |pages=147–154
 |arxiv=astro-ph/0601261
 |bibcode=2005NatPh...1..147W
 |citeseerx=10.1.1.336.2176
 |doi=10.1038/nphys172
|s2cid=118974639
 }}</ref><ref name="science304">
{{cite journal
 |last1=Gilmore |first1=G.
 |year=2004
 |title=The Short Spectacular Life of a Superstar
 |journal=[[Science (journal)|Science]]
 |volume=304 |issue=5679 |pages=1915–1916
 |doi=10.1126/science.1100370
 |pmid=15218132
|s2cid=116987470
 }}</ref> The star becomes layered like an onion, with the burning of more easily fused elements occurring in larger shells.<ref name=heger/><ref name="hinshaw">
{{cite book
 |last1=Faure |first1=G.
 |last2=Mensing |first2=T. M.
 |year=2007
 |chapter=Life and Death of Stars
 |title=Introduction to Planetary Science
 |pages=35–48
 |doi=10.1007/978-1-4020-5544-7_4
 |isbn=978-1-4020-5233-0
}}</ref> Although popularly described as an onion with an iron core, the least massive supernova progenitors only have oxygen-[[neon]](-[[magnesium]]) cores. These [[super-AGB star]]s may form the majority of core collapse supernovae, although less luminous and so less commonly observed than those from more massive progenitors.<ref name="superagb"/>

If core collapse occurs during a supergiant phase when the star still has a hydrogen envelope, the result is a type II supernova.<ref name=Horiuchi_et_al_2014>{{cite journal |bibcode=2014MNRAS.445L..99H |arxiv=1409.0006 |doi=10.1093/mnrasl/slu146|title=The red supergiant and supernova rate problems: Implications for core-collapse supernova physics |year=2014 |last1=Horiuchi |first1=S. |last2=Nakamura |first2=K. |last3=Takiwaki |first3=T. |last4=Kotake |first4=K. |last5=Tanaka |first5=M. |journal=Monthly Notices of the Royal Astronomical Society: Letters |volume=445 |pages=L99–L103 |doi-access=free }}</ref> The rate of mass loss for luminous stars depends on the metallicity and [[luminosity]]. Extremely luminous stars at near solar metallicity will lose all their hydrogen before they reach core collapse and so will not form a supernova of type II.<ref name=Horiuchi_et_al_2014/> At low metallicity, all stars will reach core collapse with a hydrogen envelope but sufficiently massive stars collapse directly to a black hole without producing a visible supernova.<ref name="heger"/>

Stars with an initial mass up to about 90 times the Sun, or a little less at high metallicity, result in a type II-P supernova, which is the most commonly observed type. At moderate to high metallicity, stars near the upper end of that mass range will have lost most of their hydrogen when core collapse occurs and the result will be a type II-L supernova.<ref>{{cite journal |doi=10.1093/mnras/stu1760 |bibcode=2014MNRAS.445..554F |arxiv=1409.1536 |title=A sample of Type II-L supernovae |year=2014 |last1=Faran |first1=T. |last2=Poznanski |first2=D. |last3=Filippenko |first3=A. V. |last4=Chornock |first4=R. |last5=Foley |first5=R. J. |last6=Ganeshalingam |first6=M. |last7=Leonard |first7=D. C. |last8=Li |first8=W. |last9=Modjaz |first9=M. |last10=Serduke |first10=F. J. D. |last11=Silverman |first11=J. M. |journal=Monthly Notices of the Royal Astronomical Society |volume=445 |issue=1 |pages=554–569 |doi-access=free }}</ref> At very low metallicity, stars of around {{Solar mass|140–250}} will reach core collapse by pair instability while they still have a hydrogen atmosphere and an oxygen core and the result will be a supernova with type II characteristics but a very large mass of ejected <sup>56</sup>Ni and high luminosity.<ref name="heger"/><ref>{{cite journal|title=Mind the Gap: The Location of the Lower Edge of the Pair-instability Supernova Black Hole Mass Gap |first1=R. |last1=Farmer |first2=M. |last2=Renzo |first3=S. E. |last3=de Mink |first4=P. |last4=Marchant |first5=S. |last5=Justham |doi=10.3847/1538-4357/ab518b |bibcode=2019ApJ...887...53F |arxiv=1910.12874 |journal=The Astrophysical Journal |year=2019 |volume=887 |number=1 |page=53 |doi-access=free }}</ref>

====Type Ib and Ic====
{{Main|Type Ib and Ic supernovae}}
[[Image:Supernova 2008D.jpg|thumb|upright=1.2|Type Ib SN 2008D<ref>
{{cite journal
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 |last24=Bayliss |first24=M. B.
 |last25=Gall |first25=C.
 |last26=Grove |first26=L. F.
 |last27=Koester |first27=B. P.
 |last28=Leitet |first28=E.
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 |last30=Skillen |first30=I.
 |year=2009
 |title=Early Spectroscopic Identification of SN 2008D
 |journal=[[The Astrophysical Journal Letters]]
 |volume=692 |issue=2 |pages=L84
 |arxiv=0805.1188
 |bibcode=2009ApJ...692L..84M
 |doi=10.1088/0004-637X/692/2/L84
|s2cid=1435322
 }}</ref> at the far upper end of the galaxy, shown in [[X-ray]] (left) and visible light (right),<ref>
{{cite journal
 |last1=Svirski |first1=G.
 |last2=Nakar |first2=E.
 |year=2014
 |title=Sn 2008D: A Wolf-Rayet Explosion Through a Thick Wind
 |journal=[[The Astrophysical Journal]]
 |volume=788 |issue=1|pages=L14
 |arxiv=1403.3400
 |bibcode=2014ApJ...788L..14S
 |doi=10.1088/2041-8205/788/1/L14
|s2cid=118395580
 }}</ref> with the brighter SN 2007uy closer to the centre]]

These supernovae, like those of type II, are massive stars that undergo core collapse. Unlike the progenitors of type II supernovae, the stars which become types Ib and Ic supernovae have lost most of their outer (hydrogen) envelopes due to strong [[stellar wind]]s or else from interaction with a companion.<ref>
{{cite conference
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 |book-title=Proceedings of the Third Pacific Rim Conference on Recent Development on Binary Star Research
 |volume=130 |pages=153–158
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 |bibcode=1997ASPC..130..153P
}}</ref> These stars are known as [[Wolf–Rayet stars]], and they occur at moderate to high metallicity where continuum driven winds cause sufficiently high mass-loss rates. Observations of type Ib/c supernova do not match the observed or expected occurrence of Wolf–Rayet stars. Alternate explanations for this type of core collapse supernova involve stars stripped of their hydrogen by binary interactions. Binary models provide a better match for the observed supernovae, with the proviso that no suitable binary helium stars have ever been observed.<ref name="eldridge">
{{cite journal
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Type Ib supernovae are the more common and result from Wolf–Rayet stars of [[Wolf-Rayet star#Classification|type WC]] which still have helium in their atmospheres. For a narrow range of masses, stars evolve further before reaching core collapse to become [[Wolf-Rayet star#Classification|WO stars]] with very little helium remaining, and these are the progenitors of type Ic supernovae.<ref>{{cite journal |doi=10.1093/mnras/stx1496|title=Towards a better understanding of the evolution of Wolf–Rayet stars and Type Ib/Ic supernova progenitors |year=2017 |last1=Yoon |first1=Sung-Chul |journal=Monthly Notices of the Royal Astronomical Society |volume=470 |issue=4 |pages=3970–3980 |doi-access=free |arxiv=1706.04716 |bibcode=2017MNRAS.470.3970Y }}</ref>

A few percent of the type Ic supernovae are associated with [[gamma-ray burst]]s (GRB), though it is also believed that any hydrogen-stripped type Ib or Ic supernova could produce a GRB, depending on the circumstances of the geometry.<ref>
{{Cite journal
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 |last6=Stockdale |first6=C. J.
 |date=2004
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 |doi=10.1111/j.1365-2966.2004.07589.x
|doi-access=free
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 }}</ref> The mechanism for producing this type of GRB is the jets produced by the magnetic field of the rapidly spinning [[magnetar]] formed at the collapsing core of the star. The jets would also transfer energy into the expanding outer shell, producing a [[super-luminous supernova]].<ref name=piram2019/><ref>
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Ultra-stripped supernovae occur when the exploding star has been stripped (almost) all the way to the metal core, via mass transfer in a close binary.<ref>
{{cite journal
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{{cite journal
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In 2022 a team of astronomers led by researchers from the Weizmann Institute of Science reported the first supernova explosion showing direct evidence for a Wolf-Rayet progenitor star. [[SN 2019hgp]] was a type Icn supernova and is also the first in which the element neon has been detected.<ref>{{cite journal |doi=10.1038/s41586-021-04155-1 |title=A WC/WO star exploding within an expanding carbon–oxygen–neon nebula |year=2022 |last1=Gal-Yam |first1=A. |last2=Bruch |first2=R. |last3=Schulze |first3=S. |last4=Yang |first4=Y. |last5=Perley |first5=D. A. |last6=Irani |first6=I. |last7=Sollerman |first7=J. |last8=Kool |first8=E. C. |last9=Soumagnac |first9=M. T. |last10=Yaron |first10=O. |last11=Strotjohann |first11=N. L. |last12=Zimmerman |first12=E. |last13=Barbarino |first13=C. |last14=Kulkarni |first14=S. R. |last15=Kasliwal |first15=M. M. |last16=De |first16=K. |last17=Yao |first17=Y. |last18=Fremling |first18=C. |last19=Yan |first19=L. |last20=Ofek |first20=E. O. |last21=Fransson |first21=C. |last22=Filippenko |first22=A. V. |last23=Zheng |first23=W. |last24=Brink |first24=T. G. |last25=Copperwheat |first25=C. M. |last26=Foley |first26=R. J. |last27=Brown |first27=J. |last28=Siebert |first28=M. |last29=Leloudas |first29=G. |last30=Cabrera-Lavers |first30=A. L. |journal=Nature |volume=601 |issue=7892 |pages=201–204 |pmid=35022591 |arxiv=2111.12435 |bibcode=2022Natur.601..201G |s2cid=244527654 }}</ref><ref>{{Cite web|title=Astronomers discover first supernova explosion of a Wolf-Rayet star|url=https://www.iac.es/en/outreach/news/astronomers-discover-first-supernova-explosion-wolf-rayet-star|access-date=9 February 2022|website=Instituto de Astrofísica de Canarias • IAC|date=12 January 2022 |language=en}}</ref>

====<span class="anchor" id="Electron-capture supernovae"></span> Electron-capture supernovae ====
In 1980, a "third type" of supernova was predicted by [[Ken'ichi Nomoto]] of the [[University of Tokyo]], called an electron-capture supernova. It would arise when a star "in the transitional range (~8 to 10 solar masses) between white dwarf formation and iron core-collapse supernovae", and with a [[degenerate matter|degenerate]] O+Ne+Mg core,<ref name=HowellEtAl2021-01a/> imploded after its core ran out of nuclear fuel, causing gravity to compress the electrons in the star's core into their atomic nuclei,<ref name=KeckObsNews2021-06-28-01a/><ref name=RTE2021-06-28-01a/> leading to a supernova explosion and leaving behind a neutron star.<ref name="heger"/> In June 2021, a paper in the journal ''[[Nature Astronomy]]'' reported that the 2018 supernova [[SN 2018zd]] (in the galaxy [[NGC 2146]], about 31 million light-years from Earth) appeared to be the first observation of an electron-capture supernova.<ref name=HowellEtAl2021-01a>{{cite journal |author1=Hiramatsu D |author2=Howell D |author3=Van S |display-authors=etal |date=28 June 2021 |title=The electron-capture origin of supernova 2018zd |url=https://www.nature.com/articles/s41550-021-01384-2 |journal=Nat Astron |volume=5 |issue=9 |pages=903–910 |doi=10.1038/s41550-021-01384-2 |arxiv=2011.02176 |bibcode=2021NatAs...5..903H |s2cid=226246044 |access-date=1 July 2021 |archive-date=30 June 2021 |archive-url=https://web.archive.org/web/20210630023436/https://www.nature.com/articles/s41550-021-01384-2 |url-status=live }}</ref><ref name=KeckObsNews2021-06-28-01a>{{cite web |url=https://keckobservatory.org/electron-capture-supernova |title=New, Third Type Of Supernova Observed |date=28 June 2021 |website=[[W. M. Keck Observatory]] |access-date=1 July 2021 |archive-date=29 June 2021 |archive-url=https://web.archive.org/web/20210629155228/https://www.keckobservatory.org/electron-capture-supernova |url-status=live }}</ref><ref name=RTE2021-06-28-01a>{{cite news|url=https://www.rte.ie/news/newslens/2021/0628/1231824-supernova-crab-nebula/|title=Astronomers discover new type of supernova|publisher=[[RTE News]]|author=|agency=[[Press Association|PA]]|date=28 June 2021|access-date=1 July 2021|quote=In 1980, Ken'ichi Nomoto of the University of Tokyo predicted a third type called an electron capture supernova. ... In an electron capture supernova, as the core runs out of fuel, gravity forces electrons in the core into their atomic nuclei, causing the star to collapse in on itself.|archive-date=30 June 2021|archive-url=https://web.archive.org/web/20210630165238/https://www.rte.ie/news/newslens/2021/0628/1231824-supernova-crab-nebula/|url-status=live}}</ref> The 1054 supernova explosion that created the Crab Nebula in our galaxy had been thought to be the best candidate for an electron-capture supernova, and the 2021 paper makes it more likely that this was correct.<ref name=KeckObsNews2021-06-28-01a/><ref name=RTE2021-06-28-01a/>

===Failed supernovae===
{{main|Failed supernova}}
The core collapse of some massive stars may not result in a visible supernova. This happens if the initial core collapse cannot be reversed by the mechanism that produces an explosion, usually because the core is too massive. These events are difficult to detect, but large surveys have detected possible candidates.<ref name=failed>
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{{cite journal
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 }}</ref> The red supergiant [[N6946-BH1]] in [[NGC 6946]] underwent a modest outburst in March 2009, before fading from view. Only a faint [[infrared]] source remains at the star's location.<ref name=adams/>

===Light curves===
[[Image:Comparative supernova type light curves.png|upright=1.75|thumb|Typical light curves for several types of supernovae; in practice, magnitude and duration varies within each type. See Karttunen et al. for types Ia, Ib, II-L and II-P;<ref name="Springer-2016">{{cite book|editor-first1=H. |editor-last1=Karttunen |editor-first2=P. |editor-last2=Kröger |editor-first3=H. |editor-last3=Oja |editor-first4=M. |editor-last4=Poutanen |editor-first5=K. J. |editor-last5=Donner |title=Fundamental Astronomy |publisher=Springer |isbn=978-3-662-53044-3 |page=309 |year=2016}}</ref> Modjaz et al. for types Ic and IIb;<ref name="Modjaz-2019">{{cite journal|first1=M. |last1=Modjaz |first2=C. P. |last2=Gutiérrez |first3=I. |last3=Arcavi |title=New regimes in the observation of core-collapse supernovae |journal=Nature Astronomy |doi=10.1038/s41550-019-0856-2 |volume=3 |date=August 2019 |issue=8 |pages=717–724|arxiv=1908.02476 |bibcode=2019NatAs...3..717M |s2cid=199472802 }}</ref> and Nyholm et al. for type IIn.<ref name="Nyholm-2020">{{cite journal|first1=A. |last1=Nyholm |display-authors=etal |title=Type IIn supernova light-curve properties measured from an untargeted survey sample |journal=Astronomy and Astrophysics |doi=10.1051/0004-6361/201936097 |volume=637 |year=2020 |page=A73|arxiv=1906.05812 |bibcode=2020A&A...637A..73N |s2cid=189762490 }}</ref>]]
The ejecta gases would dim quickly without some energy input to keep them hot. The source of this energy—which can maintain the optical supernova glow for months—was, at first, a puzzle. Some considered rotational energy from the central pulsar as a source.<ref>{{Cite journal |last1=Michel |first1=F. Curtis |last2=Kennel |first2=C. F. |last3=Fowler |first3=William A. |date=1987-11-13 |title=When Will a Pulsar in Supernova 1987a Be Seen? |journal=Science |volume=238 |issue=4829 |pages=938–940 |doi=10.1126/science.238.4829.938|pmid=17829358 |bibcode=1987Sci...238..938M |s2cid=46408677 }}</ref> Although the energy that initially powers each type of supernovae is delivered promptly, the light curves are dominated by subsequent radioactive heating of the rapidly expanding ejecta. The intensely radioactive nature of the ejecta gases was first calculated on sound nucleosynthesis grounds in the late 1960s, and this has since been demonstrated as correct for most supernovae.<ref>{{cite journal
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It is now known by direct observation that much of the light curve (the graph of luminosity as a function of time) after the occurrence of a [[type II Supernova]], such as SN 1987A, is explained by those predicted radioactive decays.<ref name=":0"/> Although the luminous emission consists of optical photons, it is the radioactive power absorbed by the ejected gases that keeps the remnant hot enough to radiate light. The radioactive decay of <sup>56</sup>Ni through its daughters <sup>56</sup>Co to <sup>56</sup>Fe produces gamma-ray [[photon]]s, primarily with energies of {{val|847|ul=keV}} and {{val|1238|u=keV|fmt=commas}}, that are absorbed and dominate the heating and thus the luminosity of the ejecta at intermediate times (several weeks) to late times (several months).<ref>
{{cite journal
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 }}</ref> Energy for the peak of the light curve of SN1987A was provided by the decay of [[Isotopes of nickel|<sup>56</sup>Ni]] to <sup>56</sup>Co (half-life 6 days) while energy for the later light curve in particular fit very closely with the 77.3-day half-life of [[Isotopes of cobalt|<sup>56</sup>Co]] decaying to <sup>56</sup>Fe. Later measurements by space gamma-ray telescopes of the small fraction of the <sup>56</sup>Co and <sup>57</sup>Co gamma rays that escaped the SN 1987A remnant without absorption confirmed earlier predictions that those two radioactive nuclei were the power sources.<ref name="S.M. Matz, G.H. Share 1988"/>

[[File:Messier 61 with SN2020jfo (Supernova).jpg|thumb|upright=1.2|[[Messier 61]] with supernova SN2020jfo, taken by an amateur astronomer in 2020]]
The late-time decay phase of visual light curves for different supernova types all depend on radioactive heating, but they vary in shape and amplitude because of the underlying mechanisms, the way that visible radiation is produced, the epoch of its observation, and the transparency of the ejected material.<ref>{{cite journal |doi=10.1051/0004-6361/201527931 |title=A two-component model for fitting light curves of core-collapse supernovae |year=2016 |last1=Nagy |first1=A. P. |last2=Vinkó |first2=J. |journal=Astronomy & Astrophysics |volume=589 |pages=A53 |arxiv=1602.04001 |bibcode=2016A&A...589A..53N |s2cid=53380594 }}</ref> The light curves can be significantly different at other wavelengths. For example, at ultraviolet wavelengths there is an early extremely luminous peak lasting only a few hours corresponding to the breakout of the shock launched by the initial event, but that breakout is hardly detectable optically.<ref>{{Cite journal |last1=Tominaga |first1=N. |last2=Blinnikov |first2=S. |last3=Baklanov |first3=P. |last4=Morokuma |first4=T. |last5=Nomoto |first5=K. |last6=Suzuki |first6=T. |date=1 November 2009 |title=Properties of Type II Plateau Supernova SNLS-04D2dc: Multicolor Light Curves of Shock Breakout and Plateau |doi-access=free |journal=The Astrophysical Journal |volume=705 |issue=1 |pages=L10–L14 |bibcode=2009ApJ...705L..10T |arxiv=0908.2162 |doi=10.1088/0004-637X/705/1/L10 |issn=0004-637X}}</ref><ref>{{Cite journal |last1=de la Rosa |first1=Janie |last2=Roming |first2=Pete |last3=Pritchard |first3=Tyler |last4=Fryer |first4=Chris |date=22 March 2016 |title=Characterizing Mid-Ultraviolet to Optical Light Curves of Nearby Type IIn Supernovae |doi-access=free |journal=The Astrophysical Journal |volume=820 |issue=1 |pages=74 |bibcode=2016ApJ...820...74D |doi=10.3847/0004-637X/820/1/74 |issn=1538-4357|hdl=1959.3/416659 |hdl-access=free }}</ref>

The light curves for type Ia are mostly very uniform, with a consistent maximum absolute magnitude and a relatively steep decline in luminosity. Their optical energy output is driven by radioactive decay of ejected nickel-56 (half-life 6 days), which then decays to radioactive cobalt-56 (half-life 77 days). These radioisotopes excite the surrounding material to incandescence.<ref name="explosion_model"/> Modern studies of cosmology rely on <sup>56</sup>Ni radioactivity providing the energy for the optical brightness of supernovae of type Ia, which are the "standard candles" of cosmology but whose diagnostic {{val|847|u=keV}} and {{val|1238|u=keV|fmt=commas}} gamma rays were first detected only in 2014.<ref>
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 |pmid=25164750
|s2cid=917374
 }}</ref> The initial phases of the light curve decline steeply as the effective size of the [[photosphere]] decreases and trapped electromagnetic radiation is depleted. The light curve continues to decline in the [[UBV photometric system|B band]] while it may show a small shoulder in the visual at about 40 days, but this is only a hint of a secondary maximum that occurs in the infra-red as certain ionised heavy elements recombine to produce infra-red radiation and the ejecta become transparent to it. The visual light curve continues to decline at a rate slightly greater than the decay rate of the radioactive cobalt (which has the longer half-life and controls the later curve), because the ejected material becomes more diffuse and less able to convert the high energy radiation into visual radiation. After several months, the light curve changes its decline rate again as [[positron emission]] from the remaining cobalt-56 becomes dominant, although this portion of the light curve has been little-studied.<ref name=taubenberger2009>{{cite journal |doi=10.1111/j.1365-2966.2009.15478.x |title=Late-time supernova light curves: The effect of internal conversion and Auger electrons |year=2009 |last1=Seitenzahl |first1=I. R. |last2=Taubenberger |first2=S. |last3=Sim |first3=S. A. |journal=Monthly Notices of the Royal Astronomical Society |volume=400 |issue=1 |pages=531–535 |doi-access=free |arxiv=0908.0247 |bibcode=2009MNRAS.400..531S |s2cid=10283901 }}</ref>

Type Ib and Ic light curves are similar to type Ia although with a lower average peak luminosity. The visual light output is again due to radioactive decay being converted into visual radiation, but there is a much lower mass of the created nickel-56. The peak luminosity varies considerably and there are even occasional type Ib/c supernovae orders of magnitude more and less luminous than the norm. The most luminous type Ic supernovae are referred to as [[hypernova]]e and tend to have broadened light curves in addition to the increased peak luminosity. The source of the extra energy is thought to be relativistic jets driven by the formation of a rotating black hole, which also produce gamma-ray bursts.<ref>
{{cite journal
 |last=Tsvetkov |first=D. Yu.
 |date=1987
 |title=Light curves of type Ib supernova: SN 1984l in NGC 991
 |journal=[[Soviet Astronomy Letters]]
 |volume=13 |pages=376–378
 |bibcode=1987SvAL...13..376T
}}</ref><ref name=arxiv>
{{cite journal
 |last=Filippenko |first=A.V.
 |date=2004
 |title=Supernovae and Their Massive Star Progenitors
 |journal=The Fate of the Most Massive Stars
 |volume=332
 |pages=34
 |arxiv=astro-ph/0412029|bibcode=2005ASPC..332...33F
}}</ref>

The light curves for type II supernovae are characterised by a much slower decline than type I, on the order of 0.05 magnitudes per day,<ref name="barbon1979">{{cite journal
 |last1=Barbon |first1=R.
 |last2=Ciatti |first2=F.
 |last3=Rosino |first3=L.
 |year=1979
 |title=Photometric properties of type II supernovae
 |journal=Astronomy and Astrophysics
 |volume=72 |pages=287
 |bibcode=1979A&A....72..287B
}}</ref> excluding the plateau phase. The visual light output is dominated by kinetic energy rather than radioactive decay for several months, due primarily to the existence of hydrogen in the ejecta from the atmosphere of the supergiant progenitor star. In the initial destruction this hydrogen becomes heated and ionised. The majority of type II supernovae show a prolonged plateau in their light curves as this hydrogen recombines, emitting visible light and becoming more transparent. This is then followed by a declining light curve driven by radioactive decay although slower than in type I supernovae, due to the efficiency of conversion into light by all the hydrogen.<ref name="doggett"/>

In type II-L the plateau is absent because the progenitor had relatively little hydrogen left in its atmosphere, sufficient to appear in the spectrum but insufficient to produce a noticeable plateau in the light output. In type IIb supernovae the hydrogen atmosphere of the progenitor is so depleted (thought to be due to tidal stripping by a companion star) that the light curve is closer to a type I supernova and the hydrogen even disappears from the spectrum after several weeks.<ref name="doggett"/>

Type IIn supernovae are characterised by additional narrow spectral lines produced in a dense shell of circumstellar material. Their light curves are generally very broad and extended, occasionally also extremely luminous and referred to as a superluminous supernova. These light curves are produced by the highly efficient conversion of kinetic energy of the ejecta into electromagnetic radiation by interaction with the dense shell of material. This only occurs when the material is sufficiently dense and compact, indicating that it has been produced by the progenitor star itself only shortly before the supernova occurs.<ref name=fillipenko1997>{{cite journal |bibcode=1997ARA&A..35..309F
|title=Optical Spectra of Supernovae
|journal=[[Annual Review of Astronomy and Astrophysics]]
|volume=35 |pages=309–355
|last1=Filippenko |first1=A. V.
|year=1997
|doi=10.1146/annurev.astro.35.1.309}}</ref><ref name=pastorello2002>{{cite journal
 | first1=A. | last1=Pastorello
 |last2=Turatto |first2=M. |last3=Benetti |first3= S. |last4=Cappellaro |first4= E. |last5=Danziger |first5= I. J. |last6=Mazzali |first6= P. A. |last7=Patat |first7= F. |last8=Filippenko |first8= A. V. |last9=Schlegel |first9=D. J. |last10= Matheson |first10= T. 
 | title=The type IIn supernova 1995G: interaction with the circumstellar medium
 | journal=Monthly Notices of the Royal Astronomical Society
 | date=2002 | volume=333 | issue=1 | pages=27–38
 | bibcode=2002MNRAS.333...27P
 | doi=10.1046/j.1365-8711.2002.05366.x | doi-access=free
 |arxiv = astro-ph/0201483 | s2cid=119347211
 }}</ref>

Large numbers of supernovae have been catalogued and classified to provide [[Standard candle|distance candles]] and test models.<ref>{{Cite journal |last1=Hauret |first1=C |last2=Magain |first2=P |last3=Biernaux |first3=J |date=21 September 2018 |title=A cosmology-independent calibration of Type Ia supernovae data |doi-access=free |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=479 |issue=3 |pages=3996–4003 |doi=10.1093/mnras/sty1715 |arxiv=1806.10900 |bibcode=2018MNRAS.479.3996H |issn=0035-8711}}</ref><ref>{{Cite journal |last1=de Jaeger |first1=T. |last2=Galbany |first2=L. |last3=González-Gaitán |first3=S. |last4=Kessler |first4=R. |last5=Filippenko |first5=A. V. |last6=Förster |first6=F. |last7=Hamuy |first7=M. |last8=Brown |first8=P. J. |last9=Davis |first9=T. M. |last10=Gutiérrez |first10=C. P. |last11=Inserra |first11=C. |last12=Lewis |first12=G. F. |last13=Möller |first13=A. |last14=Scolnic |first14=D. |last15=Smith |first15=M. |date=11 July 2020 |title=Studying Type II supernovae as cosmological standard candles using the Dark Energy Survey |doi-access=free |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=495 |issue=4 |pages=4860–4892 |doi=10.1093/mnras/staa1402 |bibcode=2018MNRAS.479.3996H |arxiv=1806.10900 |issn=0035-8711}}</ref> Average characteristics vary somewhat with distance and type of host galaxy, but can broadly be specified for each supernova type.
{|class="wikitable" style="max-width: 600px"
|+Physical properties of supernovae by type<ref name="weidong">
{{Cite journal
 |last1=Li |first1=W.
 |last2=Leaman |first2=J.
 |last3=Chornock |first3=R.
 |last4=Filippenko |first4=A. V.
 |last5=Poznanski |first5=D.
 |last6=Ganeshalingam |first6=M.
 |last7=Wang |first7=X.
 |last8=Modjaz |first8=M.
 |last9=Jha |first9=S.
 |last10=Foley |first10=R. J.
 |last11=Smith |first11=N.
 |year=2011
 |title=Nearby supernova rates from the Lick Observatory Supernova Search – II. The observed luminosity functions and fractions of supernovae in a complete sample
 |journal=Monthly Notices of the Royal Astronomical Society
 |volume=412 |issue=3 |pages=1441
 |arxiv=1006.4612
 |bibcode=2011MNRAS.412.1441L
 |doi=10.1111/j.1365-2966.2011.18160.x
|doi-access=free
 |s2cid=59467555
 }}</ref><ref name="richardson">
{{Cite journal 
 |last1=Richardson |first1=D. 
 |last2=Branch |first2=D. 
 |last3=Casebeer |first3=D. 
 |last4=Millard |first4=J. 
 |last5=Thomas |first5=R. C. 
 |last6=Baron |first6=E. 
 |year=2002 
 |title=A Comparative Study of the Absolute Magnitude Distributions of Supernovae 
 |journal=The Astronomical Journal 
 |volume=123 |issue=2 |pages=745–752 
 |arxiv=astro-ph/0112051 
 |bibcode=2002AJ....123..745R
 |doi=10.1086/338318
|s2cid=5697964 
 }}</ref>
!Type{{ref|a|a}} !!Average peak [[absolute magnitude]]{{ref|b|b}} !!Approximate energy ([[Foe (unit)|foe]]){{ref|c|c}} !!Days to peak luminosity !!Days from peak to 10% luminosity
|-
|Ia ||style="text-align:right"|−19 ||style="text-align:right"|1 ||style="text-align:right"|approx. 19 ||style="text-align:right"|around 60
|-
|Ib/c (faint) ||style="text-align:right"|around −15 ||style="text-align:right"|0.1 ||style="text-align:right"|15–25 ||style="text-align:right"|unknown
|-
|Ib ||style="text-align:right"|around −17 ||style="text-align:right"|1 ||style="text-align:right"|15–25 ||style="text-align:right"|40–100
|-
|Ic ||style="text-align:right"|around −16 ||style="text-align:right"|1 ||style="text-align:right"|15–25 ||style="text-align:right"|40–100
|-
|Ic (bright) ||style="text-align:right"|to −22 ||style="text-align:right"|above 5 ||style="text-align:right"|roughly 25 ||style="text-align:right"|roughly 100
|-
|II-b ||style="text-align:right"|around −17 ||style="text-align:right"|1 ||style="text-align:right"|around 20 ||style="text-align:right"|around 100
|-
|II-L ||style="text-align:right"|around −17 ||style="text-align:right"|1 ||style="text-align:right"|around 13 ||style="text-align:right"|around 150
|-
|II-P (faint) ||style="text-align:right"|around −14 ||style="text-align:right"|0.1 ||style="text-align:right"|roughly 15 ||style="text-align:right"|unknown
|-
|II-P ||style="text-align:right"|around −16 ||style="text-align:right"|1 ||style="text-align:right"|around 15 ||style="text-align:right"|Plateau then around 50
|-
|IIn{{ref|d|d}} ||style="text-align:right"|around −17 ||style="text-align:right"|1 ||style="text-align:right"|12–30 or more ||style="text-align:right"|50–150
|-
|IIn (bright) ||style="text-align:right"|to −22 ||style="text-align:right"|above 5 ||style="text-align:right"|above 50 ||style="text-align:right"|above 100
|}
Notes:
{{ordered list | list-style-type = lower-alpha |
| {{note|a}}Faint types may be a distinct sub-class. Bright types may be a continuum from slightly over-luminous to hypernovae.
| {{note|b}}These magnitudes are measured in the R band. Measurements in V or B bands are common and will be around half a magnitude brighter for supernovae.
| {{note|c}}[[Order of magnitude]] kinetic energy. Total electromagnetic radiated energy is usually lower, (theoretical) neutrino energy much higher.
| {{note|d}}Probably a heterogeneous group, any of the other types embedded in nebulosity.
}}

===Asymmetry===
[[Image:Chandra-crab.jpg|thumb|The [[pulsar]] in the [[Crab Nebula]] is travelling at 375 km/s relative to the nebula.<ref>
{{Cite journal
 |last1=Frail |first1=D. A.
 |last2=Giacani |first2=E. B.
 |last3=Goss |first3=W. Miller
 |last4=Dubner |first4=G. M.
 |date=1996
 |title=The Pulsar Wind Nebula Around PSR B1853+01 in the Supernova Remnant W44
 |journal=[[Astrophysical Journal Letters]]
 |volume=464 |issue=2 |pages=L165–L168
 |arxiv=astro-ph/9604121
 |bibcode=1996ApJ...464L.165F
 |doi=10.1086/310103
|s2cid=119392207
 }}</ref>]]
A long-standing puzzle surrounding type II supernovae is why the remaining compact object receives a large velocity away from the epicentre;<ref name="Höflich-2004">
{{Cite book |first=Dong |last=Lai |editor-last1=Höflich |editor-first1=P. A. |title=Cosmic explosions in three dimensions: Asymmetries in supernovae and gamma-ray bursts |editor-last2=Kumar |editor-first2=P. |editor-last3=Wheeler |editor-first3=J. Craig |date=2004 |publisher=[[Cambridge University Press]] |isbn=0-521-84286-7 |page=276 |chapter=Neutron star kicks and supernova asymmetry |bibcode=2004cetd.conf..276L |arxiv=astro-ph/0312542}}</ref> [[pulsar]]s, and thus neutron stars, are observed to have high [[Peculiar velocity|peculiar velocities]], and black holes presumably do as well, although they are far harder to observe in isolation. The initial impetus can be substantial, propelling an object of more than a solar mass at a velocity of 500&nbsp;km/s or greater. This indicates an expansion asymmetry, but the mechanism by which momentum is transferred to the compact object {{As of|2023|alt=remains}} a puzzle. Proposed explanations for this kick include convection in the collapsing star, asymmetric ejection of matter during [[neutron star formation]], and asymmetrical [[neutrino]] emissions.<ref name="Höflich-2004"/><ref name="Janka-2022">{{Cite journal |last1=Janka |first1=Hans-Thomas |last2=Wongwathanarat |first2=Annop |last3=Kramer |first3=Michael |date=1 February 2022 |title=Supernova Fallback as Origin of Neutron Star Spins and Spin-kick Alignment |doi-access=free |journal=The Astrophysical Journal |volume=926 |issue=1 |pages=9 |doi=10.3847/1538-4357/ac403c |bibcode=2022ApJ...926....9J |arxiv=2104.07493 |issn=0004-637X}}</ref>

One possible explanation for this asymmetry is large-scale [[convection]] above the core. The convection can create radial variations in density giving rise to variations in the amount of energy absorbed from neutrino outflow.<ref name="Janka-2007"/> However analysis of this mechanism predicts only modest momentum transfer.<ref name=Fryer-2004>
{{Cite journal
 |last=Fryer |first=C. L.
 |date=2004
 |title=Neutron Star Kicks from Asymmetric Collapse
 |journal=[[Astrophysical Journal]]
 |volume=601 |issue=2 |pages=L175–L178
 |arxiv=astro-ph/0312265
 |bibcode=2004ApJ...601L.175F
 |doi=10.1086/382044
|s2cid=1473584
 }}</ref> Another possible explanation is that accretion of gas onto the central neutron star can create a [[accretion disk|disk]] that drives highly directional jets, propelling matter at a high velocity out of the star, and driving transverse shocks that completely disrupt the star. These jets might play a crucial role in the resulting supernova.<ref>
{{cite journal
 |last1=Gilkis |first1=A.
 |last2=Soker |first2=N.
 |year=2014
 |title=Implications of turbulence for jets in core-collapse supernova explosions
 |journal=The Astrophysical Journal
 |volume=806 |issue=1 |page=28
 |arxiv=1412.4984
 |doi=10.1088/0004-637X/806/1/28
 |bibcode=2015ApJ...806...28G
|s2cid=119002386
 }}</ref><ref>
{{cite journal
 |last1=Khokhlov |first1=A. M.
 |last2=Höflich |first2=P. A.
 |last3=Oran |first3=E. S.
 |last4=Wheeler |first4=J. Craig
 |last5=Wang |first5=L.
 |last6=Chtchelkanova |first6=A. Yu.
 |year=1999
 |title=Jet-induced Explosions of Core Collapse Supernovae
 |journal=The Astrophysical Journal
 |volume=524 |issue=2 |pages=L107
 |arxiv=astro-ph/9904419
 |bibcode=1999ApJ...524L.107K
 |doi=10.1086/312305
|s2cid=37572204
 }}</ref> (A similar model is used for explaining long gamma-ray bursts.) The dominant mechanism may depend upon the mass of the progenitor star.<ref name="Janka-2022"/>

Initial asymmetries have also been confirmed in type Ia supernovae through observation. This result may mean that the initial luminosity of this type of supernova depends on the viewing angle. However, the expansion becomes more symmetrical with the passage of time. Early asymmetries are detectable by measuring the polarisation of the emitted light.<ref>
{{cite journal
 |last1=Wang |first1=L.
 |last2=Baade |first2=D.
 |last3=Höflich |first3=P. A.
 |last4=Khokhlov |first4=A. M.
 |last5=Wheeler |first5=J. C.
 |last6=Kasen |first6=D.
 |last7=Nugent |first7=P. E.
 |last8=Perlmutter |first8=S. A.
 |last9=Fransson |first9=C.
 |last10=Lundqvist |first10=P.
 |year=2003
 |title=Spectropolarimetry of SN 2001el in NGC 1448: Asphericity of a Normal Type Ia Supernova
 |journal=The Astrophysical Journal
 |volume=591 |issue=2 |pages=1110–1128
 |arxiv=astro-ph/0303397
 |bibcode=2003ApJ...591.1110W 
 |doi=10.1086/375444
|s2cid=2923640
 }}</ref>

===Energy output===
[[Image:SNIacurva.png|thumb|The radioactive decays of nickel-56 and cobalt-56 that produce a supernova visible light curve<ref name="explosion_model"/><ref name="mazzali"/>]]
Although supernovae are primarily known as luminous events, the [[electromagnetic radiation]] they release is almost a minor side-effect. Particularly in the case of core collapse supernovae, the emitted electromagnetic radiation is a tiny fraction of the total energy released during the event.<ref>{{cite journal |doi=10.1126/science.1075935 |title=The Secrets Behind Supernovae |year=2002 |last1=Janka |first1=H.-Th. |journal=Science |volume=297 |issue=5584 |pages=1134–1135 |pmid=12183617 |s2cid=34349443 }}</ref>

There is a fundamental difference between the balance of energy production in the different types of supernova. In type Ia white dwarf detonations, most of the energy is directed into [[nucleosynthesis|heavy element synthesis]] and the [[kinetic energy]] of the ejecta.<ref>{{cite journal |doi=10.1126/science.276.5317.1378|title=Type Ia Supernovae: Their Origin and Possible Applications in Cosmology |year=1997 |last1=Nomoto |first1=Ken'Ichi |last2=Iwamoto |first2=Koichi |last3=Kishimoto |first3=Nobuhiro |journal=Science |volume=276 |issue=5317 |pages=1378–1382 |pmid=9190677 |arxiv=astro-ph/9706007 |bibcode=1997Sci...276.1378N |s2cid=2502919 }}</ref> In core collapse supernovae, the vast majority of the energy is directed into [[supernova neutrino|neutrino]] emission, and while some of this apparently powers the observed destruction, 99%+ of the neutrinos escape the star in the first few minutes following the start of the collapse.<ref name="Antonioli-2004"/>

Standard type Ia supernovae derive their energy from a runaway nuclear fusion of a carbon-oxygen white dwarf. The details of the energetics are still not fully understood, but the result is the ejection of the entire mass of the original star at high kinetic energy. Around half a solar mass of that mass is [[nickel-56|<sup>56</sup>Ni]] generated from [[Silicon-burning process|silicon burning]]. <sup>56</sup>Ni is [[radioactive]] and decays into [[cobalt-56|<sup>56</sup>Co]] by [[beta plus decay]] (with a [[half life]] of six days) and gamma rays. <sup>56</sup>Co itself decays by the beta plus ([[positron]]) path with a half life of 77 days into stable <sup>56</sup>Fe. These two processes are responsible for the electromagnetic radiation from type Ia supernovae. In combination with the changing transparency of the ejected material, they produce the rapidly declining light curve.<ref name="mazzali"/>

Core collapse supernovae are on average visually fainter than type Ia supernovae,<ref name="Springer-2016"/><ref name="Modjaz-2019"/><ref name="Nyholm-2020"/> but the total energy released is far higher, as outlined in the following table.

{|class="wikitable"
|+Energetics of supernovae
!Supernova !!Approximate total energy<br/>x10<sup>44</sup> joules ([[Foe (unit)|foe]]){{ref|c|c}} !!Ejected Ni<br/>(solar masses) !!Neutrino energy<br/>(foe) !!Kinetic energy<br/>(foe) !!Electromagnetic radiation<br/>(foe)
|-
|Type Ia<ref name="mazzali">{{Cite journal
 |last1=Mazzali
 |first1=P. A.
 |last2=Nomoto
 |first2=K. I.
 |last3=Cappellaro
 |first3=E.
 |last4=Nakamura
 |first4=T.
 |last5=Umeda
 |first5=H.
 |last6=Iwamoto
 |first6=K.
 |year=2001
 |title=Can Differences in the Nickel Abundance in Chandrasekhar-Mass Models Explain the Relation between the Brightness and Decline Rate of Normal Type Ia Supernovae?
 |journal=The Astrophysical Journal
 |volume=547
 |issue=2
 |pages=988
 |arxiv=astro-ph/0009490
 |bibcode=2001ApJ...547..988M
 |doi=10.1086/318428 |doi-access=free
 |s2cid=9324294
 }}</ref><ref>
{{Cite journal
 |last1=Iwamoto |first1=K.
 |year=2006
 |title=Neutrino Emission from Type Ia Supernovae
 |journal=AIP Conference Proceedings
 |volume=847 |pages=406–408
 |doi=10.1063/1.2234440
|bibcode=2006AIPC..847..406I
 }}</ref><ref>
{{Cite journal
 |last1=Hayden |first1=B. T.
 |last2=Garnavich |first2=P. M.
 |last3=Kessler |first3=R.
 |last4=Frieman |first4=J. A.
 |last5=Jha |first5=S. W.
 |last6=Bassett |first6=B.
 |last7=Cinabro |first7=D.
 |last8=Dilday |first8=B.
 |last9=Kasen |first9=D.
 |last10=Marriner |first10=J.
 |last11=Nichol |first11=R. C.
 |last12=Riess |first12=A. G.
 |last13=Sako |first13=M.
 |last14=Schneider |first14=D. P.
 |last15=Smith |first15=M.
 |last16=Sollerman |first16=J.
 |year=2010
 |title=The Rise and Fall of Type Ia Supernova Light Curves in the SDSS-II Supernova Survey
 |journal=The Astrophysical Journal
 |volume=712 |issue=1 |pages=350–366
 |arxiv=1001.3428
 |bibcode=2010ApJ...712..350H
 |doi=10.1088/0004-637X/712/1/350
|s2cid=118463541
 }}</ref> ||style="text-align:right"|1.5 ||style="text-align:right"|0.4 – 0.8 ||style="text-align:right"|0.1 ||style="text-align:right"|1.3 – 1.4 ||style="text-align:right"|~0.01
|-
|Core collapse<ref>
{{cite journal
 |last1=Janka |first1=H.-T.
 |year=2012
 |title=Explosion Mechanisms of Core-Collapse Supernovae
 |journal=[[Annual Review of Nuclear and Particle Science]]
 |volume=62 |issue=1 |pages=407–451
 |arxiv=1206.2503
 |bibcode=2012ARNPS..62..407J
 |doi=10.1146/annurev-nucl-102711-094901|doi-access=free
|s2cid=118417333
 }}</ref><ref>
{{cite journal
 |last1=Smartt |first1=Stephen J.
 |last2=Nomoto |first2=Ken'ichi
 |last3=Cappellaro |first3=Enrico
 |last4=Nakamura |first4=Takayoshi
 |last5=Umeda |first5=Hideyuki
 |last6=Iwamoto |first6=Koichi
 |date=2009
 |title=Progenitors of core-collapse supernovae
 |journal=[[Annual Review of Astronomy and Astrophysics]]
 |volume=47 |issue=1 |pages=63–106
 |arxiv=0908.0700
 |bibcode=2009ARA&A..47...63S
 |doi=10.1146/annurev-astro-082708-101737
|s2cid=55900386
 }}</ref> ||style="text-align:right"|100 ||style="text-align:right"|(0.01) – 1 ||style="text-align:right"|100 ||style="text-align:right"|1 ||style="text-align:right"|0.001 – 0.01
|-
|Hypernova ||style="text-align:right"|100 ||style="text-align:right"|~1 ||style="text-align:right"|1–100 ||style="text-align:right"|1–100 ||style="text-align:right"|~0.1
|-
|Pair instability<ref name=kasen/> ||style="text-align:right"|5–100 ||style="text-align:right"|0.5 – 50 ||style="text-align:right"|low? ||style="text-align:right"|1–100 ||style="text-align:right"|0.01 – 0.1
|}

In some core collapse supernovae, fallback onto a black hole drives [[relativistic jet]]s which may produce a brief energetic and directional burst of gamma rays and also transfers substantial further energy into the ejected material. This is one scenario for producing high-luminosity supernovae and is thought to be the cause of type Ic hypernovae and long-duration gamma-ray bursts.<ref>{{Cite journal |last1=Dessart |first1=L. |last2=Burrows |first2=A. |last3=Livne |first3=E. |last4=Ott |first4=C. D. |date=20 January 2008 |title=The Proto-Neutron Star Phase of the Collapsar Model and the Route to Long-Soft Gamma-Ray Bursts and Hypernovae |doi-access=free |journal=The Astrophysical Journal |language=en |volume=673 |issue=1 |pages=L43–L46 |bibcode=2008ApJ...673L..43D |arxiv=0710.5789 |doi=10.1086/527519 |issn=0004-637X}}</ref> If the relativistic jets are too brief and fail to penetrate the stellar envelope then a low-luminosity gamma-ray burst may be produced and the supernova may be sub-luminous.<ref>{{Cite journal |last1=Senno |first1=Nicholas |last2=Murase |first2=Kohta |last3=Mészáros |first3=Peter |date=8 April 2016 |title=Choked jets and low-luminosity gamma-ray bursts as hidden neutrino sources |url=https://link.aps.org/doi/10.1103/PhysRevD.93.083003 |journal=Physical Review D |language=en |volume=93 |issue=8 |pages=083003 |doi=10.1103/PhysRevD.93.083003 |bibcode=2016PhRvD..93h3003S |arxiv=1512.08513 |s2cid=16452722 |issn=2470-0010}}</ref>

When a supernova occurs inside a small dense cloud of circumstellar material, it will produce a shock wave that can efficiently convert a high fraction of the kinetic energy into electromagnetic radiation. Even though the initial energy was entirely normal the resulting supernova will have high luminosity and extended duration since it does not rely on exponential radioactive decay. This type of event may cause type IIn hypernovae.<ref>{{Cite journal |last1=Woosley |first1=S. E. |last2=Blinnikov |first2=S. |last3=Heger |first3=Alexander |date=15 November 2007 |title=Pulsational pair instability as an explanation for the most luminous supernovae |url=https://www.nature.com/articles/nature06333 |journal=Nature |language=en |volume=450 |issue=7168 |pages=390–392 |bibcode=2007Natur.450..390W |arxiv=0710.3314 |doi=10.1038/nature06333 |pmid=18004378 |s2cid=2925738 |issn=0028-0836}}</ref><ref>{{Cite journal |last1=Barkov |first1=Maxim V. |last2=Komissarov |first2=Serguei S. |date=21 July 2011 |title=Recycling of neutron stars in common envelopes and hypernova explosions: Recycling of neutron stars and hypernovae |doi-access=free |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=415 |issue=1 |pages=944–958 |doi=10.1111/j.1365-2966.2011.18762.x |bibcode=2011MNRAS.415..944B |arxiv=1012.4565 }}</ref>

Although pair-instability supernovae are core collapse supernovae with spectra and light curves similar to type II-P, the nature after core collapse is more like that of a giant type Ia with runaway fusion of carbon, oxygen and silicon. The total energy released by the highest-mass events is comparable to other core collapse supernovae but neutrino production is thought to be very low, hence the kinetic and electromagnetic energy released is very high. The cores of these stars are much larger than any white dwarf and the amount of radioactive nickel and other heavy elements ejected from their cores can be orders of magnitude higher, with consequently high visual luminosity.<ref>{{Cite journal |last1=Wright |first1=Warren P. |last2=Gilmer |first2=Matthew S. |last3=Fröhlich |first3=Carla |last4=Kneller |first4=James P. |date=13 November 2017 |title=Neutrino signal from pair-instability supernovae |url=https://link.aps.org/doi/10.1103/PhysRevD.96.103008 |journal=Physical Review D |language=en |volume=96 |issue=10 |pages=103008 |bibcode=2017PhRvD..96j3008W |arxiv=1706.08410 |doi=10.1103/PhysRevD.96.103008 |s2cid=119487775 |issn=2470-0010}}</ref>

===Progenitor===
[[File:Artist's impression time-lapse of distant supernovae.webm|thumb|Occasional supernovae appear in this sped-up artist's impression of distant galaxies. Each exploding star briefly rivals the brightness of its host galaxy.]]
The supernova classification type is closely tied to the type of progenitor star at the time of the collapse. The occurrence of each type of supernova depends on the star's metallicity, since this affects the strength of the stellar wind and thereby the rate at which the star loses mass.<ref>{{Cite journal |last1=Ganss |first1=R |last2=Pledger |first2=J L |last3=Sansom |first3=A E |last4=James |first4=P A |last5=Puls |first5=J |last6=Habergham-Mawson |first6=S M |date=22 March 2022 |title=Metallicity estimation of core-collapse Supernova H ii regions in galaxies within 30 Mpc |doi-access=free|journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=512 |issue=1 |pages=1541–1556 |doi=10.1093/mnras/stac625 |issn=0035-8711 |bibcode=2022MNRAS.512.1541G |arxiv=2203.03308 }}</ref>

Type Ia supernovae are produced from white dwarf stars in binary star systems and occur in all [[Galaxy morphological classification|galaxy types]].<ref>{{Cite journal |last1=Prochaska |first1=J. X. |last2=Bloom |first2=J. S. |last3=Chen |first3=H.-W. |last4=Foley |first4=R. J. |last5=Perley |first5=D. A. |last6=Ramirez-Ruiz |first6=E. |last7=Granot |first7=J. |last8=Lee |first8=W. H. |last9=Pooley |first9=D. |last10=Alatalo |first10=K. |last11=Hurley |first11=K. |last12=Cooper |first12=M. C. |last13=Dupree |first13=A. K. |last14=Gerke |first14=B. F. |last15=Hansen |first15=B. M. S. |date=10 May 2006 |title=The Galaxy Hosts and Large-Scale Environments of Short-Hard Gamma-Ray Bursts |doi-access=free |journal=The Astrophysical Journal |language=en |volume=642 |issue=2 |pages=989–994 |doi=10.1086/501160 |issn=0004-637X |bibcode=2006ApJ...642..989P |arxiv=astro-ph/0510022 }}</ref> Core collapse supernovae are only found in galaxies undergoing current or very recent star formation, since they result from short-lived massive stars. They are most commonly found in type Sc spirals, but also in the arms of other spiral galaxies and in [[irregular galaxy|irregular galaxies]], especially [[Starburst galaxy|starburst galaxies]].<ref>{{Cite journal |last1=Petrosian |first1=Artashes |last2=Navasardyan |first2=Hripsime |last3=Cappellaro |first3=Enrico |last4=McLean |first4=Brian |last5=Allen |first5=Ron |last6=Panagia |first6=Nino |last7=Leitherer |first7=Claus |last8=MacKenty |first8=John |last9=Turatto |first9=Massimo |date=March 2005 |title=Active and Star-forming Galaxies and Their Supernovae |doi-access=free |journal=The Astronomical Journal |language=en |volume=129 |issue=3 |pages=1369–1380 |doi=10.1086/427712 |bibcode=2005AJ....129.1369P |issn=0004-6256}}</ref><ref>{{Cite journal |last1=Shao |first1=X. |last2=Liang |first2=Y. C. |last3=Dennefeld |first3=M. |last4=Chen |first4=X. Y. |last5=Zhong |first5=G. H. |last6=Hammer |first6=F. |last7=Deng |first7=L. C. |last8=Flores |first8=H. |last9=Zhang |first9=B. |last10=Shi |first10=W. B. |last11=Zhou |first11=L. |date=25 July 2014 |title=Comparing the Host Galaxies of Type Ia, Type II, and Type Ibc Supernovae |doi-access=free |journal=The Astrophysical Journal |volume=791 |issue=1 |pages=57 |doi=10.1088/0004-637X/791/1/57 |bibcode=2014ApJ...791...57S |arxiv=1407.0483 |issn=0004-637X}}</ref><ref>{{Cite journal |last1=Taggart |first1=K |last2=Perley |first2=D A |date=5 April 2021 |title=Core-collapse, superluminous, and gamma-ray burst supernova host galaxy populations at low redshift: the importance of dwarf and starbursting galaxies |doi-access=free |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=503 |issue=3 |pages=3931–3952 |bibcode=2021MNRAS.503.3931T |arxiv=1911.09112 |doi=10.1093/mnras/stab174 |issn=0035-8711}}</ref>

Type Ib and Ic supernovae are hypothesised to have been produced by core collapse of massive stars that have lost their outer layer of hydrogen and helium, either via strong stellar winds or mass transfer to a companion.<ref name="arxiv"/> They normally occur in regions of new star formation, and are extremely rare in [[Elliptical galaxy|elliptical galaxies]].<ref name="Perets-2010"/> The progenitors of type IIn supernovae also have high rates of mass loss in the period just prior to their explosions.<ref>{{Cite journal |last1=Moriya |first1=Takashi J. |last2=Maeda |first2=Keiichi |last3=Taddia |first3=Francesco |last4=Sollerman |first4=Jesper |last5=Blinnikov |first5=Sergei I. |last6=Sorokina |first6=Elena I. |date=11 April 2014 |title=Mass-loss histories of Type IIn supernova progenitors within decades before their explosion |doi-access=free |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=439 |issue=3 |pages=2917–2926 |bibcode=2014MNRAS.439.2917M |arxiv=1401.4893 |doi=10.1093/mnras/stu163 |issn=1365-2966}}</ref> Type Ic supernovae have been observed to occur in regions that are more metal-rich and have higher star-formation rates than average for their host galaxies.<ref>{{Cite journal |last1=Galbany |first1=L. |last2=Anderson |first2=J. P. |last3=Sánchez |first3=S. F. |last4=Kuncarayakti |first4=H. |last5=Pedraz |first5=S. |last6=González-Gaitán |first6=S. |last7=Stanishev |first7=V. |last8=Domínguez |first8=I. |last9=Moreno-Raya |first9=M. E. |last10=Wood-Vasey |first10=W. M. |last11=Mourão |first11=A. M. |last12=Ponder |first12=K. A. |last13=Badenes |first13=C. |last14=Mollá |first14=M. |last15=López-Sánchez |first15=A. R. |date=13 March 2018 |title=PISCO: The PMAS/PPak Integral-field Supernova Hosts Compilation |doi-access=free |journal=The Astrophysical Journal |volume=855 |issue=2 |pages=107 |doi=10.3847/1538-4357/aaaf20 |bibcode=2018ApJ...855..107G |arxiv=1802.01589 |issn=1538-4357}}</ref> The table shows the progenitor for the main types of core collapse supernova, and the approximate proportions that have been observed in the local neighbourhood.
{|class="wikitable"
|+ Fraction of core collapse supernovae types by progenitor<ref name=eldridge/>
|-
! Type !! Progenitor star !! Fraction
|-
|Ib ||WC [[Wolf–Rayet star|Wolf–Rayet]] or [[helium star]] ||9.0%
|-
|Ic ||WO [[Wolf–Rayet star|Wolf–Rayet]] ||17.0%
|-
|II-P ||[[Supergiant]] ||55.5%
|-
|II-L ||[[Supergiant]] with a depleted hydrogen shell ||3.0%
|-
|IIn ||[[Supergiant]] in a dense cloud of expelled material (such as [[Luminous blue variable|LBV]])||2.4%
|-
|IIb ||[[Supergiant]] with highly depleted hydrogen (stripped by companion?) ||12.1%
|-
|IIpec ||[[Blue supergiant]]||1.0%
|}

[[File:Supernovae as initial mass-metallicity.svg|upright=1.8|thumb|Supernova types by initial mass-metallicity]]
[[File:Remnants of single massive stars.svg|upright=1.8|thumb|Remnants of single massive stars]]

There are a number of difficulties reconciling modelled and observed stellar evolution leading up to core collapse supernovae. Red supergiants are the progenitors for the vast majority of core collapse supernovae, and these have been observed but only at relatively low masses and luminosities, below about {{solar mass|18}} and {{solar luminosity|100,000}}, respectively. Most progenitors of type II supernovae are not detected and must be considerably fainter, and presumably less massive. This discrepancy has been referred to as the '''red supergiant problem'''.<ref name="davies2020"/> It was first described in 2009 by Stephen Smartt, who also coined the term. After performing a volume-limited search for supernovae, Smartt et al. found the lower and upper mass limits for type II-P supernovae to form to be {{solar mass|{{val|8.5|1|1.5}}}} and {{solar mass|{{val|16.5|1.5}}}}, respectively. The former is consistent with the expected upper mass limits for white dwarf progenitors to form, but the latter is not consistent with massive star populations in the Local Group.<ref name=smartt2009>{{Cite journal |last1=Smartt |first1=S. J. |last2=Eldridge |first2=J. J. |last3=Crockett |first3=R. M. |last4=Maund |first4=J. R. |date=May 2009 |title=The death of massive stars – I. Observational constraints on the progenitors of Type II-P supernovae |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=395 |issue=3 |pages=1409–1437 |arxiv=0809.0403 |bibcode=2009MNRAS.395.1409S |doi=10.1111/j.1365-2966.2009.14506.x |doi-access=free |s2cid=3228766 |issn=0035-8711}}</ref> The upper limit for red supergiants that produce a visible supernova explosion has been calculated at {{val|19|4|2|u=solar mass}}.<ref name=davies2020>{{cite journal |bibcode=2020MNRAS.496L.142D |arxiv=2005.13855 |doi=10.1093/mnrasl/slaa102 |title='On the red supergiant problem': A rebuttal, and a consensus on the upper mass cut-off for II-P progenitors |year=2020 |last1=Davies |first1=Ben |last2=Beasor |first2=Emma R. |journal=Monthly Notices of the Royal Astronomical Society: Letters |volume=496 |issue=1 |pages=L142–L146 |doi-access=free }}</ref>

It is thought that higher mass red supergiants do not explode as supernovae, but instead evolve back towards hotter temperatures. Several progenitors of type IIb supernovae have been confirmed, and these were K and G supergiants, plus one A supergiant.<ref name=smartt/> Yellow hypergiants or LBVs are proposed progenitors for type IIb supernovae, and almost all type IIb supernovae near enough to observe have shown such progenitors.<ref name=problem>
{{Cite journal
 |last1=Walmswell |first1=J. J.
 |last2=Eldridge |first2=J. J.
 |doi=10.1111/j.1365-2966.2011.19860.x
 |title=Circumstellar dust as a solution to the red supergiant supernova progenitor problem
 |journal=Monthly Notices of the Royal Astronomical Society
 |volume=419 |issue=3 |pages=2054
 |year=2012
|doi-access=free
 |arxiv=1109.4637
 |bibcode=2012MNRAS.419.2054W
|s2cid=118445879
 }}</ref><ref name=ysg>
{{Cite journal
 |last1=Georgy |first1=C.
 |doi=10.1051/0004-6361/201118372
 |title=Yellow supergiants as supernova progenitors: An indication of strong mass loss for red supergiants?
 |journal=Astronomy & Astrophysics
 |volume=538 |pages=L8–L2 |year=2012
|arxiv=1111.7003 |bibcode=2012A&A...538L...8G
|s2cid=55001976
 }}</ref>
[[File:Stellar evolution v2024.png|alt=Infographic showing arrows between circles representing stellar evolution and how it varies by mass|thumb|Approximate stellar evolution pathways of supernova progenitor stars (and lower mass stars) with circle size reflecting relative size and color related to temperature]]
Blue supergiants form an unexpectedly high proportion of confirmed supernova progenitors, partly due to their high luminosity and easy detection, while not a single Wolf–Rayet progenitor has yet been clearly identified.<ref name=smartt>
{{cite journal
|bibcode=2009ARA&A..47...63S
|title=Progenitors of Core-Collapse Supernovae
|journal=[[Annual Review of Astronomy & Astrophysics]]
|volume=47 |issue=1 |pages=63–106
|year=2009 |doi=10.1146/annurev-astro-082708-101737
|arxiv=0908.0700
|last1=Smartt
|first1=Stephen J.
|last2=Thompson
|first2=Todd A.
|last3=Kochanek
|first3=Christopher S.
|s2cid=55900386
}}</ref><ref name=yoon/> Models have had difficulty showing how blue supergiants lose enough mass to reach supernova without progressing to a different evolutionary stage. One study has shown a possible route for low-luminosity post-red supergiant luminous blue variables to collapse, most likely as a type IIn supernova.<ref name=lbv>
{{Cite journal
 |last1=Groh |first1=J. H.
 |last2=Meynet |first2=G.
 |last3=Ekström |first3=S.
 |title=Massive star evolution: Luminous blue variables as unexpected supernova progenitors
 |doi=10.1051/0004-6361/201220741
 |journal=Astronomy & Astrophysics
 |volume=550 |pages=L7 |year=2013
|arxiv=1301.1519
 |bibcode=2013A&A...550L...7G
|s2cid=119227339
 }}</ref> Several examples of hot luminous progenitors of type IIn supernovae have been detected: [[SN 2005gy]] and [[SN 2010jl]] were both apparently massive luminous stars, but are very distant; and [[SN 2009ip]] had a highly luminous progenitor likely to have been an LBV, but is a peculiar supernova whose exact nature is disputed.<ref name=smartt/>

The progenitors of type Ib/c supernovae are not observed at all, and constraints on their possible luminosity are often lower than those of known [[WC star]]s.<ref name=smartt/> [[WO star]]s are extremely rare and visually relatively faint, so it is difficult to say whether such progenitors are missing or just yet to be observed. Very luminous progenitors have not been securely identified, despite numerous supernovae being observed near enough that such progenitors would have been clearly imaged.<ref name=yoon>
{{cite journal
|bibcode=2012A&A...544L..11Y
|title=On the nature and detectability of Type Ib/c supernova progenitors
|journal=Astronomy & Astrophysics
|volume=544|pages=L11
|year=2012
|doi=10.1051/0004-6361/201219790
|arxiv=1207.3683|last1=Yoon
|first1=S.-C.
|last2=Gräfener
|first2=G.
|last3=Vink
|first3=J. S.
|last4=Kozyreva
|first4=A.
|last5=Izzard
|first5=R. G.
|s2cid=118596795
}}</ref> Population modelling shows that the observed type Ib/c supernovae could be reproduced by a mixture of single massive stars and stripped-envelope stars from interacting binary systems.<ref name=eldridge/> The continued lack of unambiguous detection of progenitors for normal type Ib and Ic supernovae may be due to most massive stars collapsing directly to a black hole [[failed supernova|without a supernova outburst]]. Most of these supernovae are then produced from lower-mass low-luminosity helium stars in binary systems. A small number would be from rapidly rotating massive stars, likely corresponding to the highly energetic type Ic-BL events that are associated with long-duration gamma-ray bursts.<ref name=smartt/>