Editing Nova

{{short description|Nuclear explosion in a white dwarf star}}
{{Redirect2|Novas|Novae|other uses|Novas (disambiguation)|and|Novae (disambiguation)|and|Nova (disambiguation)}}
{{distinguish|luminous red nova|supernova|kilonova|micronova}}
{{Use dmy dates|date=November 2020}}
[[Image:Making a Nova.jpg|frame|right|Artist's conception of a white dwarf, right, [[Accretion (astrophysics)|accreting]] hydrogen from the [[Roche lobe]] of its larger companion star]]

A '''nova''' ({{plural form}} '''novae''' or '''novas''') is a [[transient astronomical event]] that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", Latin for "new") that slowly fades over weeks or months. All observed novae involve [[white dwarf]]s in close [[binary star|binary system]]s, but causes of the dramatic appearance of a nova vary, depending on the circumstances of the two progenitor stars. The main sub-classes of novae are classical novae, recurrent novae (RNe), and [[dwarf nova]]e. They are all considered to be [[cataclysmic variable star]]s.

Classical nova eruptions are the most common type. This type is usually created in a close binary star system consisting of a white dwarf and either a [[main sequence]], [[subgiant]], or [[red giant star]]. If the orbital period of the system is a few days or less, the white dwarf is close enough to its companion star to draw [[accretion (astrophysics)|accreted]] [[matter]] onto its surface, creating a dense but shallow [[Stellar atmosphere|atmosphere]]. This atmosphere, mostly consisting of [[hydrogen]], is heated by the hot white dwarf and eventually reaches a critical temperature, causing ignition of rapid [[thermal runaway|runaway]] [[nuclear fusion|fusion]]. The sudden increase in energy expels the atmosphere into interstellar space, creating the envelope seen as visible light during the nova event. In past centuries such an event was thought to be a new star. A few novae produce short-lived [[nova remnant]]s, lasting for perhaps several centuries.

A recurrent nova involves the same processes as a classical nova, except that the nova event repeats in cycles of a few decades or less as the companion star again feeds the dense atmosphere of the white dwarf after each ignition, as in the star [[T Coronae Borealis]].

Under certain conditions, mass accretion can eventually trigger runaway fusion that destroys the white dwarf rather than merely expelling its atmosphere. In this case, the event is usually classified as a [[Type Ia supernova]].

Novae most often occur in the sky along the path of the [[Milky Way]], especially near the observed [[Galactic Center]] in Sagittarius; however, they can appear anywhere in the sky. They occur far more [[List of novae in the Milky Way galaxy|frequently]] than galactic [[supernova]]e, averaging about ten per year in the Milky Way. Most are found telescopically, perhaps only one every 12–18 months reaching [[naked eye|naked-eye]] visibility. Novae reaching first or second [[magnitude (astronomy)|magnitude]] occur only a few times per century. The last bright nova was [[V1369 Centauri]], which reached 3.3 magnitude on 14 December 2013.<ref>{{Cite web|title=Nova Centauri 2013: Another bright, naked-eye nova {{!}} aavso.org|url=https://www.aavso.org/nova-centauri-2013-another-bright-naked-eye-nova|access-date=2020-11-02|website=www.aavso.org}}</ref>

== Etymology ==
During the sixteenth century, astronomer [[Tycho Brahe]] observed the [[supernova]] [[SN 1572]] in the [[constellation]] [[Cassiopeia (constellation)|Cassiopeia]]. He described it in his book ''De nova stella'' ([[Latin]] for "concerning the new star"), giving rise to the adoption of the name ''nova''. In this work he argued that a nearby object should be seen to move relative to the fixed stars, and thus the nova had to be very far away. Although SN 1572 was later found to be a supernova and not a nova, the terms were considered interchangeable until the 1930s.<ref name="encyc" /> After this, novae were called ''classical novae'' to distinguish them from [[supernova]]e, as their causes and energies were thought to be different, based solely on the observational evidence.

Although the term "stella nova" means "new star", novae most often take place on [[white dwarf]]s, which are remnants of extremely old stars.

== Stellar evolution of novae ==
[[File:Nova-Eridani-2009-LB4.jpg|thumb|right|[[KT Eridani|Nova Eridani 2009]] ([[apparent magnitude]] ~8.4)]]
Evolution of potential novae begins with two [[main sequence]] stars in a binary system. One of the two [[Stellar evolution|evolves]] into a [[red giant]], leaving its remnant white dwarf core in orbit with the remaining star. The second star—which may be either a [[Main sequence|main-sequence star]] or an aging [[Giant star|giant]]—begins to shed its envelope onto its white dwarf companion when it overflows its [[Roche lobe]]. As a result, the white dwarf steadily captures matter from the companion's outer atmosphere in an accretion disk, and in turn, the accreted matter falls into the atmosphere. As the white dwarf consists of [[degenerate matter]], the [[Accretion (astrophysics)|accreted]] [[hydrogen]] is unable to expand even though its temperature increases. Runaway fusion occurs when the temperature of this atmospheric layer reaches ~20&nbsp;million [[Kelvin|K]], initiating nuclear burning via the [[CNO cycle]].<ref>{{cite journal |title= On the Progenitors of Galactic Novae |journal= The Astrophysical Journal |date= 10 February 2012 |volume= 746 |issue= 61 |pages= 61 |author= M.J. Darnley |display-authors= etal |doi=10.1088/0004-637x/746/1/61 |bibcode=2012ApJ...746...61D|arxiv = 1112.2589 |s2cid= 119291027 }}</ref>

If the accretion rate is just right, hydrogen fusion may occur in a stable manner on the surface of the white dwarf, giving rise to a [[super soft X-ray source]], but for most binary system parameters, the hydrogen burning is thermally unstable and rapidly converts a large amount of the hydrogen into other, [[Weight|heavier]] [[chemical element]]s in a [[thermal runaway|runaway]] reaction,<ref name="encyc">{{cite book|chapter=Novae|date=2001|editor=Paul Murdin|first=Dina|isbn=978-1-56159-268-5|last=Prialnik|pages=1846–1856|publisher=[[Institute of Physics Publishing]]/[[Nature Publishing Group]]|title=Encyclopedia of Astronomy and Astrophysics}}</ref> liberating an enormous amount of energy. This blows the remaining gases away from the surface of the white dwarf and produces an extremely bright outburst of light.

The rise to peak brightness may be very rapid, or gradual; after the peak, the brightness declines steadily.<ref>[[AAVSO]] Variable Star Of The Month: [http://www.aavso.org/vstar/vsots/0501.shtml May 2001: Novae] {{Webarchive|url=https://web.archive.org/web/20031106083823/http://www.aavso.org/vstar/vsots/0501.shtml |date=6 November 2003 }}</ref> The time taken for a nova to decay by 2 or 3&nbsp;magnitudes from maximum optical brightness is used for grouping novae into speed classes. Fast novae typically will take less than 25&nbsp;days to decay by 2&nbsp;magnitudes, while slow novae will take more than 80&nbsp;days.<ref>
{{cite book
 | first= Brian | last = Warner
 | date = 1995
 | title = Cataclysmic Variable Stars
 | isbn = 978-0-521-41231-5
 | publisher = [[Cambridge University Press]]
}}</ref>

Despite its violence, usually the amount of [[material]] ejected in a nova is only about {{frac|10,000}} of a [[solar mass]], quite small relative to the mass of the white dwarf. Furthermore, only five percent of the accreted mass is fused during the power outburst.<ref name="encyc" /> Nonetheless, this is enough energy to accelerate nova ejecta to velocities as high as several thousand kilometers per second—higher for fast novae than slow ones—with a concurrent rise in [[luminosity]] from a few times solar to 50,000–100,000&nbsp;times solar.<ref name="encyc" /><ref>

{{cite book
 |last=Zeilik |first=Michael
 |date=1993
 |title=Conceptual Astronomy
 |publisher=[[John Wiley & Sons]]
 |isbn=978-0-471-50996-7
}}</ref> In 2010 scientists using NASA's [[Fermi Gamma-ray Space Telescope]] discovered that a nova also can emit [[gamma ray]]s (>100&nbsp;MeV).<ref>
{{cite web
 |author=[[JPL]]/[[NASA]]
 |date=12 August 2010
 |title=Fermi detects 'shocking' surprise from supernova's little cousin
 |url=http://www.physorg.com/news200849593.html
 |work=[[PhysOrg]]
 |access-date=15 August 2010
}}</ref>

Potentially, a [[white dwarf]] can generate multiple novae over time as additional [[hydrogen]] continues to accrete onto its surface from its [[Binary star|companion star]]. Where this repeated flaring is observed, the object is called a recurrent nova. An example is [[RS Ophiuchi]], which is known to have flared seven times (in 1898, 1933, 1958, 1967, 1985, 2006, and 2021). Eventually, the [[white dwarf]] can [[Explosion|explode]] as a [[Type Ia supernova|Type&nbsp;Ia supernova]] if it approaches the [[Chandrasekhar limit]].

Occasionally, novae are bright enough and close enough to Earth to be conspicuous to the unaided eye. The brightest recent example was [[V1500 Cygni|Nova Cygni 1975]]. This nova appeared on 29&nbsp;August 1975, in the constellation [[Cygnus (constellation)|Cygnus]] about 5 degrees north of [[Deneb]], and reached [[Apparent magnitude|magnitude]]&nbsp;2.0 (nearly as bright as [[Deneb]]). The most recent were [[V1280 Scorpii]], which reached magnitude&nbsp;3.7 on 17&nbsp;February 2007, and [[Nova Delphini 2013]]. [[Nova Centauri 2013]] was discovered 2&nbsp;December 2013 and so far is the brightest nova of this [[millennium]], reaching magnitude&nbsp;3.3.

=== Helium novae ===
A [[helium]] nova (undergoing a [[helium flash]]) is a proposed category of nova event that lacks [[Hydrogen spectral series|hydrogen lines]] in its [[Spectral line|spectrum]]. The absence of [[hydrogen]] lines may be caused by the [[explosion]] of a [[helium]] shell on a [[white dwarf]]. The [[theory]] was first proposed in 1989, and the first candidate [[helium]] nova to be observed was [[V445 Puppis]], in 2000.<ref>{{cite journal
 | author=Kato, Mariko
 | author2=Hachisu, Izumi
 | title=V445 Puppis: Helium Nova on a Massive White Dwarf
 | journal=The Astrophysical Journal | volume=598 | issue=2 | pages=L107–L110
 |date=December 2005
 | doi=10.1086/380597
 | bibcode=2003ApJ...598L.107K
|arxiv = astro-ph/0310351 | s2cid=17055772
 }}</ref> Since then, four other novae have been proposed as [[helium]] novae.<ref>{{cite journal
 | title=List of Helium Novae
 | last=Rosenbush | first=A. E.
 | journal=Hydrogen-Deficient Stars
 | volume=391| pages=271 | date=17–21 September 2007
 | location=Eberhard Karls University, Tübingen, Germany
 | editor=Klaus Werner |editor2=Thomas Rauch
 | publication-date=July 2008
 | bibcode=2008ASPC..391..271R
}}</ref>

== Occurrence rate and astrophysical significance ==

Astronomers have estimated that the [[Milky Way]] experiences roughly 25 to 75 novae per year.<ref name="Shafter2017">{{cite journal
|last1=Shafter 
|first1=A.W.
|title=The Galactic Nova Rate Revisited
|journal=The Astrophysical Journal | volume=834 | issue=2 | pages=192–203
|date=January 2017
|doi=10.3847/1538-4357/834/2/196
|bibcode=2017ApJ...834..196S
|arxiv=1606.02358|s2cid=118652484
|doi-access=free
}}</ref> The number of novae actually observed in the Milky Way each year is much lower, about 10,<ref name=nova_list>
{{cite web
 |title=CBAT List of Novae in the Milky Way
 |url=http://cbat.eps.harvard.edu/nova_list.html
 |publisher=IAU [[Central Bureau for Astronomical Telegrams]]
}}</ref> probably because distant novae are obscured by gas and dust absorption.<ref name="nova_list"/> As of 2019, 407 probable novae had been recorded in the Milky Way.<ref name="nova_list" /> In the [[Andromeda Galaxy]], roughly 25 novae brighter than about 20th magnitude are discovered each year, and smaller numbers are seen in other nearby galaxies.<ref name="M31-Nova">
{{cite web
 |title=M31 (Apparent) Novae Page
 |url=http://cbat.eps.harvard.edu/CBAT_M31.html
 |publisher=IAU [[Central Bureau for Astronomical Telegrams]]
 |access-date=2009-02-24
}}</ref>

[[Spectroscopy|Spectroscopic]] observation of nova ejecta [[nebulae]] has shown that they are enriched in elements such as helium, carbon, nitrogen, oxygen, neon, and magnesium.<ref name="encyc" /> Classical nova [[explosion]]s are galactic producers of the element [[lithium]].<ref name="EA-20200601">{{cite news |author=[[Arizona State University]] |date=1 June 2020 |title=Class of stellar explosions found to be galactic producers of lithium |url=https://www.eurekalert.org/pub_releases/2020-06/asu-cos060120.php |access-date=2 June 2020 |work=[[EurekAlert!]]}}</ref><ref name="AJ-20200527">{{cite journal |author=Starrfield, Sumner |author1-link=Sumner Starrfield |display-authors=et al. |date=27 May 2020 |title=Carbon–Oxygen Classical Novae Are Galactic 7Li Producers as well as Potential Supernova Ia Progenitors |journal=[[The Astrophysical Journal]] |volume=895 |page=70 |arxiv=1910.00575 |bibcode=2020ApJ...895...70S |doi=10.3847/1538-4357/ab8d23 |s2cid=203610207 |doi-access=free |number=1}}</ref> The contribution of novae to the [[interstellar medium]] is not great; novae supply only {{frac|50}} as much material to the galaxy as do supernovae, and only {{frac|200}} as much as [[red giant]] and [[supergiant]] stars.<ref name="encyc" />

Observed recurrent novae such as [[RS Ophiuchi]] (those with periods on the order of decades) are rare. Astronomers theorize, however, that most, if not all, novae recur, albeit on time scales ranging from 1,000 to 100,000 years.<ref>
{{cite book
 |last=Seeds |first=Michael A.
 |date=1998
 |title=Horizons: Exploring the Universe
 |page=194 |edition=5th
 |publisher=[[Wadsworth Publishing Company]]
 |isbn=978-0-534-52434-0
}}</ref> The recurrence interval for a nova is less dependent on the accretion rate of the white dwarf than on its mass; with their powerful gravity, massive white dwarfs require less accretion to fuel an eruption than lower-mass ones.<ref name="encyc" /> Consequently, the interval is shorter for high-mass white dwarfs.<ref name="encyc" />

[[V Sagittae]] is unusual in that the time of its next eruption can be predicted fairly accurately; it is expected to recur in approximately 2083, plus or minus about 11 years.<ref>{{Cite web|url=https://phys.org/news/2020-01-binary-star-sagittae-bright-nova.html|title=Binary star V Sagittae to explode as very bright nova by century's end|website=phys.org|language=en-us|access-date=2020-01-20}}</ref>

=== Subtypes ===
Novae are classified according to the [[light curve]] decay speed, referred to as either type A, B, C and R,<ref>{{Cite web |title=Overview: Long-term visual light curves {{!}} aavso |url=https://www.aavso.org/overview-long-term-visual-light-curves |access-date=2024-07-14 |website=www.aavso.org}}</ref> or using the prefix "N": 
* '''NA''': fast novae, with a rapid brightness increase, followed by a brightness decline of 3 magnitudes—to about {{frac|16}} brightness—within 100 days.<ref name="heasarc">
{{cite web
 |date=31 March 2010
 |title=Ritter Cataclysmic Binaries Catalog (7th Edition, Rev. 7.13)
 |publisher=[[High Energy Astrophysics Science Archive Research Center]]
 |url=http://heasarc.gsfc.nasa.gov/W3Browse/all/rittercv.html
 |access-date=2010-09-25
}}</ref>
* '''NB''': slow novae, with a brightness decline of 3 magnitudes in 150 days or more.
* '''NC''': very slow novae, also known as [[symbiotic nova]]e, staying at maximum light for a decade or more and then fading very slowly.
* '''NR'''/'''RN''': recurrent novae, where two or more eruptions separated by 80 years or less have been observed.<ref>{{Cite web |title=GCVS Variability Types and Distribution Statistics of Designated Variable Stars According to their Types of Variability |url=https://cdsarc.u-strasbg.fr/ftp/cats/B/gcvs/vartype.txt |website=VizieR archive server, Strasbourg astronomical Data Center (CDS)}}</ref> These are generally also fast.

==Remnants==
[[File:GKPersei-MiniSuperNova-20150316.jpg|thumb|250px|right|[[GK Persei]]: Nova of 1901]]
{{main|Nova remnant}}
Some novae leave behind visible [[nebulosity]], material expelled in the nova explosion or in multiple explosions.<ref name="Liimets2014">{{Cite book
|last1=Liimets
|first1=T.
|last2=Corradi
|first2=R.L.M.
|last3=Santander-García
|first3=M. 
|last4=Villaver
|first4=E.
|last5=Rodríguez-Gil
|first5=P.
|last6=Verro
|first6=K.
|last7=Kolka
|first7=I.
|year=2014
|chapter=A Dynamical Study of the Nova Remnant of GK Persei / Stella Novae: Past and Future Decades. 
|title=Stellar Novae: Past and Future Decades
|series=ASP Conference Series
|volume=490
|pages=109–115
|arxiv=1310.4488
|bibcode=2014ASPC..490..109L}}</ref>

== Novae as distance indicators ==
Novae have some promise for use as [[standard candle]] measurements of distances. For instance, the distribution of their [[absolute magnitude]] is [[bimodal distribution|bimodal]], with a main peak at magnitude −8.8, and a lesser one at −7.5. Novae also have roughly the same absolute magnitude 15 days after their peak (−5.5). Nova-based distance estimates to various nearby [[Galaxy|galaxies]] and [[galaxy cluster]]s have been shown to be of comparable accuracy to those measured with [[Cepheid]] [[variable star]]s.<ref>
{{cite book
 |last1=Robert |first1=Gilmozzi
 |last2=Della Valle |first2=Massimo
 |date=2003
 |chapter=Novae as Distance Indicators
 |editor-last=Alloin |editor-first=D.
 |editor2-last=Gieren
 |title=Stellar Candles for the Extragalactic Distance Scale
 |url=https://archive.org/details/stellarcandlesfo00allo |url-access=limited |pages=[https://archive.org/details/stellarcandlesfo00allo/page/n241 229]–241
 |publisher=[[Springer (publisher)|Springer]]
 |isbn=978-3-540-20128-1 |editor2-first=W.
}}</ref>

== Recurrent novae<!--'Recurrent nova', 'Recurrent novae', 'Recurrent Nova', and 'Recurrent Novae' redirect here--> ==
A '''recurrent nova'''<!--boldface per WP:R#PLA--> ('''RN''')<!--boldface per MOS:BOLDSYN--> is an object that has been seen to experience repeated nova eruptions. The recurrent nova typically brightens by about 9 magnitudes, whereas a classical nova may brighten by more than 12 magnitudes.<ref name=Schaefer2009>
{{cite journal
 |last=Schaefer |first=Bradley E.
 |year=2010
 |title=Comprehensive Photometric Histories of All Known Galactic Recurrent Novae
 |arxiv=0912.4426
 |doi=10.1088/0067-0049/187/2/275
 |volume=187
 |issue=2
 |journal=The Astrophysical Journal Supplement Series
 |pages=275–373
 |bibcode = 2010ApJS..187..275S |s2cid=119294221
 }}</ref>

Although it is estimated that as many as a quarter of nova systems experience multiple eruptions, only ten recurrent novae (listed below) have been observed in the Milky Way.<ref>{{cite journal |bibcode=2014ApJ...788..164P |title=Identifying and Quantifying Recurrent Novae Masquerading as Classical Novae |last1=Pagnotta |first1=Ashley |last2=Schaefer |first2=Bradley E. |journal=The Astrophysical Journal |year=2014 |volume=788 |issue=2 |page=164 |doi=10.1088/0004-637X/788/2/164 |arxiv=1405.0246 |s2cid=118448146 }}</ref>

Several [[Extragalactic astronomy|extragalactic]] recurrent novae have been observed in the [[Andromeda Galaxy]] (M31) and the [[Large Magellanic Cloud]]. One of these extragalactic novae, [[M31N 2008-12a]], erupts as frequently as once every 12 months.

On 20 April 2016, the ''[[Sky & Telescope]]'' website reported a sustained brightening of [[T Coronae Borealis]] from magnitude 10.5 to about 9.2 starting in February 2015. A similar event had been reported in 1938, followed by another outburst in 1946.<ref name=sandt>{{cite web |url=http://www.skyandtelescope.com/observing/whats-up-with-t-crb04202016 |publisher=Sky & Telescope website |title=Is T CrB About to Blow its Top?|date=20 April 2016 |accessdate=2017-08-06}}</ref> By June 2018, the star had dimmed slightly but still remained at an unusually high level of activity. In March or April 2023, it dimmed to magnitude 12.3.<ref>{{cite web |last1=Schaefer |first1=B.E. |last2=Kloppenborg |first2=B. |last3=Waagen |first3=E.O. |title=Announcing T CrB pre-eruption dip |url=https://www.aavso.org/news/t-crb-pre-eruption-dip |website=AAVSO |publisher=American Association of Variable Star Observers |access-date=18 January 2024}}</ref> A similar dimming occurred in the year before the 1945 outburst, indicating that it would likely erupt between March and September 2024.<ref>{{cite web |last1=Todd |first1=Ian |title=T Coronae Borealis nova event guide and how to prepare |url=https://www.skyatnightmagazine.com/space-science/t-coronae-borealis-nova |website=Sky at Night Magazine |publisher=BBC |access-date=18 March 2024}}</ref> {{As of|2025|2|10|post=,}} this predicted outburst has not yet occurred.

{{Clear|left}}

{| class="wikitable sortable" text-align:center;"
|-----
! Full name
! Discoverer
! Distance ([[light-year|ly]])
! [[Apparent magnitude|Magnitude]]<br/> range
! Days to drop<br/> 3&nbsp;magnitudes<br/> from peak
! Known eruption years
! Interval (years)
! Years since latest eruption
|-----
| [[CI Aquilae]]
| [[Karl Wilhelm Reinmuth|K. Reinmuth]]
| {{val|8590|830}}
| 8.6–16.3
| 40
| 1917, 1941, 2000
| 24–59
|bgcolor=#84CF65|{{age in years|2000|04|30}}
|-----
| [[V394 Coronae Australis]]
| [[Luis Enrique Erro|L. E. Erro]]
| {{val|17000|3000}}<ref>{{cite journal |last1=Hachisu |first1=Izumi |last2=Kato |first2=Mariko |title=A Theoretical Light-Curve Model for the Recurrent Nova V394 Coronae Australis |journal=The Astrophysical Journal |date=September 2000 |volume=540 |issue=1 |pages=447–451 |doi=10.1086/309338 |arxiv=astro-ph/0003471 |bibcode=2000ApJ...540..447H |url=https://iopscience.iop.org/article/10.1086/309338 |access-date=3 May 2024}}</ref>
| 7.2–19.7
| 6
| 1949, 1987
| 38
|bgcolor=#E2EB20|{{age in years|1987|07|30}}
|-----
| [[T Coronae Borealis]]
| [[John Birmingham (astronomer)|J. Birmingham]]
| {{val|2987|75}}
| 2.5–10.8
| 6
| 1217, 1787, 1866, 1946
| 80
|bgcolor=#E2EB20|{{age in years|1946|02|09}}
|-----
| [[IM Normae]]
| [[Ida E. Woods|I. E. Woods]]
| {{val|9800|1600}}<ref>{{cite journal |last1=Patterson |first1=Joseph |last2=Kemp |first2=Jonathan |last3=Monard |first3=Berto |last4=Myers |first4=Gordon |last5=de Miguel |first5=Enrique |last6=Hambsch |first6=Franz-Josef |last7=Warhurst |first7=Paul |last8=Rea |first8=Robert |last9=Dvorak |first9=Shawn |last10=Menzies |first10=Kenneth |last11=Vanmunster |first11=Tonny |last12=Roberts |first12=George |last13=Campbell |first13=Tut |last14=Starkey |first14=Donn |last15=Ulowetz |first15=Joseph |last16=Rock |first16=John |last17=Seargeant |first17=Jim |last18=Boardman |first18=James |last19=Lemay |first19=Damien |last20=Cejudo |first20=David |last21=Knigge |first21=Christian |title=IM Normae: The Death Spiral of a Cataclysmic Variable? |journal=The Astrophysical Journal |date=1 January 2022 |volume=924 |issue=1 |pages=27 |doi=10.3847/1538-4357/abec87 |doi-access=free |bibcode=2022ApJ...924...27P |arxiv=2010.07812 }}</ref>
| 8.5–18.5
| 70
| 1920, 2002
| ≤82
|bgcolor=#84CF65|{{age in years|2002|01|14}}
|-----
| [[RS Ophiuchi]]
| [[Williamina Fleming|W. Fleming]]
| {{val|8740|850}}
| 4.8–11
| 14
| 1898, 1907, 1933, 1958, 1967, 1985, 2006, 2021
| 9–26
|bgcolor=#84CF65|{{age in years|2021|08|08}}
|-----
| [[V2487 Ophiuchi]]
| [[Kesao Takamizawa|K. Takamizawa]] (1998)
| {{val|20900|5200}}<ref>{{cite journal |last1=Rodríguez-Gil |first1=Pablo |last2=Corral-Santana |first2=Jesús M |last3=Elías-Rosa |first3=N |last4=Gänsicke |first4=Boris T |last5=Hernanz |first5=Margarita |last6=Sala |first6=Gloria |title=The orbital period of the recurrent nova V2487 Oph revealed |journal=Monthly Notices of the Royal Astronomical Society |date=20 October 2023 |volume=526 |issue=4 |pages=4961–4975 |doi=10.1093/mnras/stad3124 |doi-access=free |url=https://academic.oup.com/mnras/article/526/4/4961/7310889 |access-date=3 May 2024|arxiv=2310.05877 }}</ref>
| 9.5–17.5
| 9
| 1900, 1998
| 98
|bgcolor=#84CF65|{{age in years|1998|06|19}}
|-----
| [[T Pyxidis]]
| [[Henrietta Swan Leavitt|H. Leavitt]]
| {{val|9410|780}}
| 6.4–15.5
| 62
| 1890, 1902, 1920, 1944, 1967, 2011
| 12–44
|bgcolor=#E2EB20|{{age in years|2011|04|14}}
|-----
| [[V3890 Sagittarii]]
| [[Harriet Dinerstein|H. Dinerstein]]
| {{val|16000}}<ref>{{cite journal |last1=Anupama |first1=G. C. |last2=Sethi |first2=S. |title=Spectroscopy of the recurrent nova V3890 Sagittarii 18 d after the 1990 outburst |journal=Monthly Notices of the Royal Astronomical Society |date=1 July 1994 |volume=269 |issue=1 |pages=105–109 |doi=10.1093/mnras/269.1.105 |doi-access=free |url=https://academic.oup.com/mnras/article/269/1/105/1004643 |access-date=3 May 2024}}</ref>
| 8.1–18.4
| 14
| 1962, 1990, 2019
| 28–29
|bgcolor=#84CF65|{{age in years|2019|08|27}}
|-----
| [[U Scorpii]]
| [[N. R. Pogson]]
| {{val|31300|2000}}<ref name="Hachisu2017">{{Cite journal |last=Hachisu |first=Izumi |last2=Kato |first2=Mariko |date=1 April 2016 |title=The UBV Color Evolution of Classical Novae. II. Color-Magnitude Diagram |journal=[[The Astrophysical Journal Supplement Series]] |volume=223 |issue=2 |pages=21 |arxiv=1602.01195 |bibcode=2016ApJS..223...21H |doi=10.3847/0067-0049/223/2/21 |doi-access=free}}</ref>
| 7.5–17.6
| 2.6
| 1863, 1906, 1917, 1936, 1979, 1987, 1999, 2010, 2022, 
| 8–43
|bgcolor=#84CF65|{{age in years|2022|06|05}}
|-----
| [[V745 Scorpii]]
| [[Lukas Plaut|L. Plaut]]
| {{val|25400|2600}}<ref name="Hachisu2017" />
| 9.4–19.3
| 7
| 1937, 1989, 2014
| 25–52
|bgcolor=#84CF65|{{age in years|2014|02|06}}
|}

== Extragalactic novae ==
[[File:Nova in M31.jpg|thumb|Nova in [[Andromeda Galaxy]]]]
Novae are relatively common in the [[Andromeda Galaxy]] (M31); several dozen novae (brighter than [[apparent magnitude]] +20) are discovered in M31 each year.<ref name="M31-Nova"/> The [[Central Bureau for Astronomical Telegrams]] (CBAT) has tracked novae in M31, [[Triangulum Galaxy|M33]], and [[Messier 81|M81]].<ref name="supernovae.net">
{{cite web
 |first=David | last = Bishop
 |title=Extragalactic Novae
 |publisher=International Supernovae Network
 |url=http://www.rochesterastronomy.org/novae.html
 |access-date=2010-09-11
}}</ref>

== See also ==
{{cmn|colwidth=20em|
* [[Cosmic distance ladder]]
* [[Crab Nebula]]
* [[Guest star (astronomy)]]
* [[Hypernova]]
* [[Kilonova]]
* [[Micronova]]
* [[Superluminous supernova]]
* [[Supernova]]
* [[Supernova impostor]]
* [[X-ray burster]]
}}
{{Clear|right}}

== References ==
{{Reflist|30em}}

== Further reading ==
*{{Cite book
 |last=Payne-Gaposchkin
 |first=Cecilia
 |url=https://archive.org/details/galacticnovae0000ceci_a7g6
 |title=The Galactic Novae
 |date=1957
 |publisher=[[North Holland Publishing Company]]
 |location=Amsterdam, NY
 |oclc=838013
 |url-access=registration
}}
*{{Cite book
 |title=Classical Nova Explosions: International Conference on Classical Nova Explosions, Sitges, Spain, 20-24 May, 2002
 |date=2002
 |publisher=[[American Institute of Physics]]
 |isbn=978-0-7354-0092-4
 |editor-last=Hernanz |editor-first=Margarita
 |editor-last2=José |editor-first2=Jordi
 |series=AIP conference proceedings
 |location=Melville, N.Y
}}
*{{Cite book
 |last=Bode |first=Michael F.
 |last2=Evans |first2=Aneurin
 |title=Classical Novae
 |date=2008
 |publisher=[[Cambridge University Press]]
 |isbn=978-0-521-84330-0
 |edition=2nd
 |series=Cambridge astrophysics series
 |location=Cambridge
}}
*{{Cite journal
 |last=Schaefer |first=Bradley E.
 |date=April 2010
 |title=Comprehensive Photometric Histories of All Known Galactic Recurrent Novae
 |journal=[[The Astrophysical Journal Supplement Series]]
 |volume=187 |issue=2 |pages=275–373
 |arxiv=0912.4426 |bibcode=2010ApJS..187..275S
 |doi=10.1088/0067-0049/187/2/275 |issn=0067-0049 |s2cid=119294221
}}
*{{Cite journal
 |last=Shafter |first=A. W.
 |display-authors=etal
 |date=10 June 2011
 |title=A Spectroscopic and Photometric Survey of Novae in M31
 |journal=[[The Astrophysical Journal]]
 |volume=734 |issue=1 |page=12
 |arxiv=1104.0222 |bibcode=2011ApJ...734...12S
 |doi=10.1088/0004-637X/734/1/12 |issn=0004-637X |s2cid=119114867
}}
*{{Cite journal
 |last=Della Valle |first=Massimo
 |last2=Izzo |first2=Luca
 |date=July 2020
 |title=Observations of galactic and extragalactic novae
 |journal=[[The Astronomy and Astrophysics Review]]
 |volume=28 |issue=1 |page=3
 |arxiv=2004.06540 |bibcode=2020A&ARv..28....3D
 |doi=10.1007/s00159-020-0124-6 |issn=0935-4956 |s2cid=215754507
}}

== External links ==
{{commons|Nova|Nova}}

* [http://www.sai.msu.su/groups/cluster/gcvs/gcvs/ General Catalog of Variable Stars], [[Sternberg Astronomical Institute]], Moscow
* [http://www.aavso.org/vstar/vsots/0501.shtml AAVSO Variable Star of the Month. Novae: May 2001] {{Webarchive|url=https://web.archive.org/web/20031106083823/http://www.aavso.org/vstar/vsots/0501.shtml |date=6 November 2003 }}
* [https://web.archive.org/web/20100408150756/http://www.supernovae.net/novae.html Extragalactic Novae]

{{Supernovae}}
{{white dwarf}}
{{Variable star topics}}
{{Portal bar|Astronomy|Stars|Outer space}}
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[[Category:Novae| ]]
[[Category:Astronomical events]]
[[Category:Stellar phenomena]]