View source for Astronomy:Luminous blue variable

{{short description|Type of star that is luminous, blue, and variable in brightness}}
[[File:AG Carinae (HD 94910).png|thumb|right|upright=1.2|Luminous blue variable AG Carinae as seen by the Hubble Space Telescope]]
'''Luminous blue variables''' ('''LBVs''') are massive evolved stars that show unpredictable and sometimes dramatic variations in their spectra and brightness. They are also known as '''S Doradus variables''' after [[Astronomy:S Doradus|S Doradus]], one of the brightest stars of the [[Astronomy:Large Magellanic Cloud|Large Magellanic Cloud]]. They are considered to be rare.

==Discovery and history==
[[Image:P Cygni Profile-en.svg|thumb|left|upright=1.1|P Cygni profile of a spectral line]]
The LBV stars [[Astronomy:P Cygni|P Cygni]] and [[Astronomy:Eta Carinae|η Carinae]] have been known as unusual variables since the 17th century, but their true nature was not fully understood until late in the 20th century.

In 1922 John Charles Duncan published the first three variable stars ever detected in an external galaxy, variables 1, 2, and 3, in the [[Astronomy:Triangulum Galaxy|Triangulum Galaxy]] (M33). These were followed up by [[Biography:Edwin Hubble|Edwin Hubble]] with three more in 1926: A, B, and C in M33. Then in 1929 Hubble added a list of variables detected in [[Astronomy:Messier 31|M31]]. Of these, Var A, Var B, Var C, and Var 2 in M33 and Var 19 in M31 were followed up with a detailed study by Hubble and [[Biography:Allan Sandage|Allan Sandage]] in 1953. Var 1 in M33 was excluded as being too faint and Var 3 had already been classified as a [[Astronomy:Cepheid variable|Cepheid variable]]. At the time they were simply described as irregular variables, although remarkable for being the brightest stars in those galaxies.<ref name=hubble-sandage>{{cite journal|bibcode=1953ApJ...118..353H|title=The Brightest Variable Stars in Extragalactic Nebulae. I. M31 and M33|journal=Astrophysical Journal|volume=118|pages=353|last1=Hubble|first1=Edwin|last2=Sandage|first2=Allan|date=1953|doi=10.1086/145764}}</ref> The original Hubble Sandage paper contains a footnote that S Doradus might be the same type of star, but expressed strong reservations, so the link would have to wait several decades to be confirmed.

Later papers referred to these five stars as Hubble–Sandage variables. In the 1970s, Var 83 in M33 and [[Astronomy:AE Andromedae|AE Andromedae]], [[Astronomy:AF Andromedae|AF Andromedae]] (=Var 19), Var 15, and Var A-1 in M31 were added to the list and described by several authors as "luminous blue variables", although it was not considered a formal name at the time. The spectra were found to contain lines with P Cygni profiles and were compared to η Carinae.<ref name=rosino>{{cite journal|bibcode=1975A&A....42..289B|title=The spectrum of the bright variable A-1 in M31|journal=Astronomy and Astrophysics|volume=42|pages=289|last1=Bianchini|first1=A.|last2=Rosino|first2=L.|date=1975}}</ref> In 1978, Roberta M. Humphreys published a study of eight variables in M31 and M33 (excluding Var A) and referred to them as luminous blue variables, as well as making the link to the S Doradus class of variable stars.<ref name=humphreys>{{cite journal|doi=10.1086/155797|title=Luminous variable stars in M31 and M33|journal=The Astrophysical Journal|volume=219|pages=445|year=1978|last1=Humphreys|first1=R. M.|bibcode=1978ApJ...219..445H|doi-access=free}}</ref> In 1984 in a presentation at the IAU symposium, Peter Conti formally grouped the S Doradus variables, Hubble–Sandage variables, η Carinae, P Cygni, and other similar stars together under the term "luminous blue variables" and shortened it to LBV. He also clearly separated them from those other luminous blue stars, the Wolf–Rayet stars.<ref name=conti>{{Cite book|bibcode=1984IAUS..105..233C|chapter=Basic Observational Constraints on the Evolution of Massive Stars|volume=105|pages=233–254|last1=Conti|first1=P. S.|title=Observational Tests of the Stellar Evolution Theory|date=1984|doi=10.1007/978-94-010-9570-9_47|isbn=978-90-277-1775-7}}</ref>

Variable star types are usually named after the first member discovered to be variable, for example δ Sct variables named after the star [[Astronomy:Delta Scuti|δ Sct]].  The first luminous blue variable to be identified as a variable star was P Cygni, and these stars have been referred to as P Cygni type variables.  The [[Astronomy:General Catalogue of Variable Stars|General Catalogue of Variable Stars]] decided there was a possibility of confusion with P Cygni profiles, which also occur in other types of stars, and chose the acronym SDOR for "variables of the S Doradus type".<ref name=sharov>{{cite book|bibcode=1975IAUS...67..275S|volume=67|pages=275–284|last1=Sharov|first1=A. S.|title=Variable Stars and Stellar Evolution |chapter=S Dor-Type Variables in Other Galaxies |year=1975|doi=10.1007/978-94-010-9934-9_38|isbn=978-90-277-0579-2}}</ref> The term "S Doradus variable" was used to describe P Cygni, S Doradus, η Carinae, and the Hubble-Sandage variables as a group in 1974.<ref name=thackaray>{{cite journal|bibcode=1974MNRAS.168..221T|title=Variations of S Dor and HDE 269006|journal=[[Organization:Monthly Notices of the Royal Astronomical Society|Monthly Notices of the Royal Astronomical Society]]|volume=168|pages=221–233|last1=Thackeray|first1=A. D.|date=1974|doi=10.1093/mnras/168.1.221|doi-access=free}}</ref>

==Physical properties==
[[File:Lbvstar.png|upright=1.5|left|thumb|Upper portion of H-R Diagram showing the location of the S Doradus instability strip and the location of LBV outbursts. Main sequence is the thin sloping line on the lower left.]]
LBVs are massive unstable [[Astronomy:Supergiant|supergiant]] (or [[Astronomy:Hypergiant|hypergiant]]) stars that show a variety of spectroscopic and photometric variation, most obviously periodic ''outburst''s and occasional much larger ''eruption''s.

In their "quiescent" state they are typically B-type stars, occasionally slightly hotter, with unusual emission lines. They are found in a region of the [[Hertzsprung–Russell diagram]] known as the [[Astronomy:S Doradus|S Doradus]] instability strip, where the least luminous have a temperature around 10,000 K and a luminosity about 250,000 times that of the Sun, whereas the most luminous have a temperature around 25,000 K and a luminosity over a million times that of the Sun, making them some of the [[Astronomy:List of most luminous stars|most luminous]] of all stars.

During a normal outburst the temperature decreases to around 8,500 K for all stars, slightly hotter than the [[Astronomy:Yellow hypergiant|yellow hypergiant]]s. The bolometric luminosity usually remains constant, which means that visual brightness increases somewhat by a magnitude or two. A few examples have been found where luminosity appears to change during an outburst, but the properties of these unusual stars are difficult to determine accurately. For example, [[Astronomy:AG Carinae|AG Carinae]] may decrease in luminosity by around 30% during outbursts; and [[Astronomy:AFGL 2298|AFGL 2298]] has been observed to dramatically increase its luminosity during an outburst although it is not clear if that should be classified as a modest ''giant eruption''.<ref name=jorick>{{cite book|last1=Vink|first1=Jorick S.|title=Eta Carinae and the Supernova Impostors|volume=384|year=2012|pages=221–247|doi=10.1007/978-1-4614-2275-4_10|chapter=Eta Carinae and the Luminous Blue Variables|series=Astrophysics and Space Science Library|isbn=978-1-4614-2274-7|bibcode=2012ASSL..384..221V|arxiv = 0905.3338 |citeseerx=10.1.1.250.4184|s2cid=17983157}}</ref>  S Doradus typifies this behaviour, which has been referred to as ''strong-active cycle'', and it is regarded as a key criterion for identifying luminous blue variables. Two distinct periodicities are seen, either variations taking longer than 20 years, or less than 10 years. In some cases, the variations are much smaller, less than half a magnitude, with only small temperature reductions. These are referred to as ''weak-active'' cycles and always occur on timescales of less than 10 years.<ref name=sterken>{{cite journal|bibcode=2003ASPC..292..437S|title=Cycles and cyclicities in Luminous Blue Variables: The S Dor phenomenon|journal=Interplay of Periodic|volume=292|pages=437|last1=Sterken|first1=C.|year=2003}}</ref>

Some LBVs have been observed to undergo giant eruptions with dramatically increased mass loss and luminosity, so violent that several were initially catalogued as supernovae. The outbursts mean there are usually [[Astronomy:Nebula|nebula]]e around such stars; [[Astronomy:Eta Carinae|η Carinae]] is the best-studied and most luminous known example, but may not be typical.<ref>{{cite arXiv|eprint=1402.0257v1|last1= Guzik|first1= Joyce A.|title= Pulsations and Hydrodynamics of Luminous Blue Variable Stars|last2=  Lovekin|first2= Catherine C.|class= astro-ph. SR|year= 2014}}</ref>  It is generally assumed that all luminous blue variables undergo one or more of these large eruptions, but they have only been observed in two or three well-studied stars and possibly a handful of supernova imposters. The two clear examples in the Milky Way galaxy, P Cygni and η Carinae, and the possible example in the Small Magellanic Cloud, HD 5980A, have not shown strong-cycle variations. It is still possible that the two types of variability occur in different groups of stars.<ref name=vangenderen>{{cite journal|last1=van Genderen|first1=A. M.|title=S Doradus variables in the Galaxy and the Magellanic Clouds|journal=Astronomy and Astrophysics|volume=366|issue=2|year=2001|pages=508–531|issn=0004-6361|doi=10.1051/0004-6361:20000022|bibcode=2001A&A...366..508V|doi-access=free}}</ref>  3-D simulations have shown that these outbursts may be caused by variations in helium opacity.<ref>{{cite journal |last1=Jiang |first1=Yan-Fei |last2=Cantiello |first2=Matteo |last3=Bildsten |first3=Lars |last4=Quataert |first4=Eliot |last5=Blaes |first5=Omer |last6=Stone |first6=James |title=Outbursts of luminous blue variable stars from variations in the helium opacity |journal=Nature |date=September 2018 |volume=561 |issue=7724 |pages=498–501 |doi=10.1038/s41586-018-0525-0 |pmid=30258134 |language=En |issn=0028-0836|arxiv=1809.10187 |bibcode=2018Natur.561..498J |s2cid=205570660 }}</ref>

Many luminous blue variables also show small amplitude variability with periods less than a year, which appears typical of Alpha Cygni variables,<ref name=jorick/> and stochastic (i.e. totally random) variations.<ref name=sterken/>

Luminous blue variables are by definition more luminous than most stars and also more massive, but within a very wide range. The most luminous are more than {{solar luminosity|a million}} (Eta Carinae reaches 4.6 million) and have masses approaching, possibly exceeding, {{solar mass|100}}. The least luminous have luminosities around {{solar luminosity|a quarter of a million}} and masses as low as {{solar mass|10}}, although they would have been considerably more massive as main-sequence stars, due to their rapid mass loss. Their high mass loss rates could be due to outbursts and very high luminosity and show some enhancement of helium and nitrogen.<ref name=jorick/>

==Evolution==
[[File:EtaCarinae-HST-1995-09.jpg|thumb|left|upright=1.0|The [[Astronomy:Homunculus Nebula|Homunculus Nebula]], produced by the Great Outburst of η Carinae]]
Because of these stars' large mass and high luminosity, their [[Astronomy:Stellar evolution|lifetime]] is very short—only a few million years in total and much less than a million years in the LBV phase.<ref name=groh0114>{{Cite journal|arxiv=1401.7322|last1=Groh|first1=Jose|title=The evolution of massive stars and their spectra I. A non-rotating 60 Msun star from the zero-age main sequence to the pre-supernova stage|journal=Astronomy & Astrophysics|volume=564|pages=A30|last2=Meynet|first2=Georges|last3=Ekstrom|first3=Sylvia|last4=Georgy|first4=Cyril|date=2014|doi=10.1051/0004-6361/201322573|bibcode=2014A&A...564A..30G|s2cid=118870118}}</ref> They are rapidly evolving on observable timescales; examples have been detected where stars with Wolf–Rayet spectra (WNL/Ofpe) have developed to show LBV outbursts and a handful of supernovae have been traced to likely LBV progenitors. Recent theoretical research confirms the latter scenario, where luminous blue variable stars are the final evolutionary stage of some massive stars before they explode as supernovae, for at least stars with initial masses between 20 and 25 [[Astronomy:Solar mass|solar mass]]es.<ref name=groh0113>{{cite journal| doi=10.1051/0004-6361/201220741| title=Massive star evolution: Luminous blue variables as unexpected supernova progenitors| journal=Astronomy & Astrophysics| volume=550| pages=L7| year=2013| last1=Groh| first1=J. H.| last2=Meynet| first2=G.| last3=Ekström| first3=S.| bibcode=2013A&A...550L...7G|arxiv = 1301.1519 | s2cid=119227339}}</ref>  For more-massive stars, computer simulations of their evolution suggest the luminous blue variable phase takes place during the latest phases of core hydrogen burning (LBV with high surface temperature), the hydrogen shell burning phase (LBV with lower surface temperature), and the earliest part of the core helium burning phase (LBV with high surface temperature again) before transitioning to the [[Astronomy:Wolf–Rayet star|Wolf–Rayet phase]],<ref name="groh2014">{{Cite journal|last1=Groh |first1=Jose |arxiv=1401.7322 |title=The evolution of massive stars and their spectra I. A non-rotating 60 Msun star from the zero-age main sequence to the pre-supernova stage |journal=Astronomy & Astrophysics |volume=564 |pages=A30 |date=2014 |last2=Meynet |first2=Georges |last3=Ekstrom |first3=Sylvia |last4=Georgy |first4=Cyril |doi=10.1051/0004-6361/201322573 |bibcode=2014A&A...564A..30G |s2cid=118870118 }}</ref> thus being analogous to the [[Astronomy:Red giant|red giant]] and [[Astronomy:Red supergiant|red supergiant]] phases of less massive stars.

There appear to be two groups of LBVs, one with luminosities above 630,000 times the Sun and the other with luminosities below 400,000 times the Sun, although this is disputed in more-recent research.<ref name=groh0813>{{cite journal|bibcode=2013A&A...558A.131G|title=Fundamental properties of core-collapse supernova and GRB progenitors: Predicting the look of massive stars before death|journal=Astronomy & Astrophysics|volume=558|pages=A131|last1=Groh|first1=Jose H.|last2=Meynet|first2=Georges|last3=Georgy|first3=Cyril|last4=Ekström|first4=Sylvia|year=2013|doi=10.1051/0004-6361/201321906|arxiv = 1308.4681 |s2cid=84177572}}</ref> Models have been constructed showing that the lower-luminosity group are post-red-supergiants with initial masses of 30–60 times the Sun, whereas the higher-luminosity group are population-II stars with initial masses 60–90 times the Sun that never develop to [[Astronomy:Red supergiant|red supergiant]]s, although they may become [[Astronomy:Yellow hypergiant|yellow hypergiant]]s.<ref name="stothers">{{cite journal|doi=10.1086/177740|title=Evolution of Massive Stars into Luminous Blue Variables and Wolf-Rayet Stars for a Range of Metallicities: Theory versus Observation|journal=The Astrophysical Journal|volume=468|pages=842|year=1996|last1=Stothers|first1=Richard B.|last2=Chin|first2=Chao-Wen|bibcode=1996ApJ...468..842S|doi-access=free}}</ref> Some models suggest that LBVs are a stage in the evolution of very massive stars required for them to shed excess mass,<ref name="smith">{{cite journal|doi=10.1086/506523|title=On the Role of Continuum-driven Eruptions in the Evolution of Very Massive Stars and Population III Stars|journal=The Astrophysical Journal|volume=645|issue=1|pages=L45|year=2006|last1=Smith|first1=Nathan|last2=Owocki|first2=Stanley P.|bibcode=2006ApJ...645L..45S|arxiv = astro-ph/0606174 |s2cid=15424181}}</ref> whereas others require that most of the mass is lost at an earlier cool-supergiant stage.<ref name="stothers"/> Normal outbursts and the stellar winds in the quiescent state are not sufficient for the required mass loss, but LBVs occasionally produce abnormally large outbursts that can be mistaken for a faint supernova and these may shed the necessary mass. Recent models all agree that the LBV stage occurs after the main-sequence stage and before the hydrogen-depleted Wolf–Rayet stage, and that essentially all LBV stars will eventually explode as supernovae. LBVs apparently can explode directly as a supernova, but probably only a small fraction do. If the star does not lose enough mass before the end of the LBV stage, it may undergo a particularly powerful supernova created by [[Astronomy:Pair-instability supernova|pair-instability]]. The latest models of stellar evolution suggest that some single stars with initial masses around 20 times that of the Sun will explode as LBVs as type II-P, type IIb, or type Ib supernovae,<ref name=groh0113/> whereas binary stars undergo much-more-complex evolution through envelope stripping leading to less predictable outcomes.<ref name=sana>{{cite journal|doi=10.1126/science.1223344|pmid=22837522|title=Binary Interaction Dominates the Evolution of Massive Stars|journal=Science|volume=337|issue=6093|pages=444–6|year=2012|last1=Sana|first1=H.|last2=De Mink|first2=S. E.|last3=De Koter|first3=A.|last4=Langer|first4=N.|last5=Evans|first5=C. J.|last6=Gieles|first6=M.|last7=Gosset|first7=E.|last8=Izzard|first8=R. G.|last9=Le Bouquin|first9=J.- B.|last10=Schneider|first10=F. R. N.|bibcode=2012Sci...337..444S|arxiv = 1207.6397 |s2cid=53596517}}</ref>

==Supernova-like outbursts==
[[File:Stars similar to Eta Carinae in nearby galaxies.jpg|thumb|upright=1.4|Stars similar to η Carinae in nearby galaxies]]
Luminous blue variable stars can undergo "giant outbursts" with dramatically increased mass loss and luminosity. η Carinae is the prototypical example,<ref name=smith_frew2011>{{cite journal|last1=Smith|first1=N.|title=A revised historical light curve of Eta Carinae and the timing of close periastron encounters|journal=Monthly Notices of the Royal Astronomical Society|volume=415|issue=3|year=2011|pages=2009–2019|last2=Frew|first2=D. J.|doi=10.1111/j.1365-2966.2011.18993.x|bibcode=2011MNRAS.415.2009S|arxiv = 1010.3719 |s2cid=118614725}}</ref> with P Cygni showing one or more similar outbursts 300–400 years ago,<ref name=humphreys1999>{{cite journal|last1=Humphreys|first1=R. M.|last2=Davidson|first2=K.|last3=Smith|first3=N.|title=Eta Carinae's Second Eruption and the Light Curves of the eta Carinae Variables|journal=Publications of the Astronomical Society of the Pacific|volume=111|issue=763|year=1999|pages=1124–1131|doi=10.1086/316420|bibcode=1999PASP..111.1124H|doi-access=free}}</ref> but dozens have now been catalogued in external galaxies. Many of these were initially classified as supernovae but re-examined because of unusual features.<ref name=imposters>{{cite journal|doi=10.1111/j.1365-2966.2011.18763.x|title=Luminous blue variable eruptions and related transients: Diversity of progenitors and outburst properties|journal=Monthly Notices of the Royal Astronomical Society|volume=415|issue=1|pages=773|year=2011|last1=Smith|first1=Nathan|last2=Li|first2=Weidong|last3=Silverman|first3=Jeffrey M.|last4=Ganeshalingam|first4=Mohan|last5=Filippenko|first5=Alexei V.|bibcode=2011MNRAS.415..773S|arxiv = 1010.3718 |s2cid=85440811}}</ref> The nature of the outbursts and of the progenitor stars seems to be highly variable,<ref name=unmasking>{{cite journal|bibcode=2012ApJ...758..142K|title=Unmasking the Supernova Impostors|journal=The Astrophysical Journal|volume=758|issue=2|pages=142|last1=Kochanek|first1=C. S.|last2=Szczygieł|first2=D. M.|last3=Stanek|first3=K. Z.|year=2012|doi=10.1088/0004-637X/758/2/142|arxiv = 1202.0281 |s2cid=118623783}}</ref> with the outbursts most likely having several different causes. The historical η Carinae and P Cygni outbursts, and several seen more recently in external galaxies, have lasted years or decades whereas some of the supernova imposter events have declined to normal brightness within months. Well-studied examples are:
* SN 1954J
* [[Astronomy:SN 1961V|SN 1961V]]
* SN 1997bs

Early models of stellar evolution had predicted that although the high-mass stars that produce LBVs would often or always end their lives as supernovae, the supernova explosion would not occur at the LBV stage. Prompted by the progenitor of [[Astronomy:SN 1987A|SN 1987A]] being a blue supergiant, and most likely an LBV, several subsequent supernovae have been associated with LBV progenitors. The progenitor of [[Astronomy:SN 2005gl|SN 2005gl]] has been shown to be an LBV apparently in outburst only a few years earlier.<ref name=2005gl>{{cite journal|doi=10.1038/nature07934|pmid=19305392|title=A massive hypergiant star as the progenitor of the supernova SN 2005gl|journal=Nature|volume=458|issue=7240|pages=865–7|year=2009|last1=Gal-Yam|first1=A.|last2=Leonard|first2=D. C.|bibcode=2009Natur.458..865G|s2cid=4392537}}</ref>  Progenitors of several other type IIn supernovae have been detected and were likely to have been LBVs:<ref name=tartaglia>{{cite journal|bibcode= 2016MNRAS.459.1039T|arxiv=1604.00013|title=Interacting supernovae and supernova impostors. LSQ13zm: An outburst heralds the death of a massive star|journal=Monthly Notices of the Royal Astronomical Society|volume=459|issue=1|pages=1039|last1=Tartaglia|first1=L.|last2=Pastorello|first2=A.|last3=Sullivan|first3=M.|last4=Baltay|first4=C.|last5=Rabinowitz|first5=D.|last6=Nugent|first6=P.|last7=Drake|first7=A. J.|last8=Djorgovski|first8=S. G.|last9=Gal-Yam|first9=A.|last10=Fabrika|first10=S.|last11=Barsukova|first11=E. A.|last12=Goranskij|first12=V. P.|last13=Valeev|first13=A. F.|last14=Fatkhullin|first14=T.|last15=Schulze|first15=S.|last16=Mehner|first16=A.|last17=Bauer|first17=F. E.|last18=Taubenberger|first18=S.|last19=Nordin|first19=J.|last20=Valenti|first20=S.|last21=Howell|first21=D. A.|last22=Benetti|first22=S.|last23=Cappellaro|first23=E.|last24=Fasano|first24=G.|last25=Elias-Rosa|first25=N.|last26=Barbieri|first26=M.|last27=Bettoni|first27=D.|last28=Harutyunyan|first28=A.|last29=Kangas|first29=T.|last30=Kankare|first30=E.|display-authors=29|year=2016|doi=10.1093/mnras/stw675|s2cid=22996021}}</ref>
* [[Astronomy:SN 2009ip|SN 2009ip]]
* SN 2010jl

Modelling suggests that at near-solar metallicity, stars with an initial mass around {{solar mass|20–25}} will explode as a supernova while in the LBV stage of their lives. They will be post-red-supergiants with luminosities a few hundred thousand times that of the Sun. The supernova is expected to be of type II, most likely type IIb, although possibly type IIn due to episodes of enhanced mass loss that occur as an LBV and in the [[Astronomy:Yellow hypergiant|yellow-hypergiant]] stage.<ref name=groh>{{cite journal|doi=10.1051/0004-6361/201220741|title=Massive star evolution: Luminous blue variables as unexpected supernova progenitors|journal=Astronomy & Astrophysics|volume=550|pages=L7|year=2013|last1=Groh|first1=J. H.|last2=Meynet|first2=G.|last3=Ekström|first3=S.|bibcode=2013A&A...550L...7G|arxiv = 1301.1519 |s2cid=119227339}}</ref>

==List of LBVs==
The identification of LBVs requires confirmation of the characteristic spectral and photometric variations, but these stars can be "quiescent" for decades or centuries at which time they are indistinguishable from many other hot luminous stars. A candidate luminous blue variable (cLBV) can be identified relatively quickly on the basis of its spectrum or luminosity, and dozens have been catalogued in the Milky Way during recent surveys.<ref name=survey>{{cite journal|doi=10.1051/0004-6361/201118040|title=The first X-ray survey of Galactic luminous blue variables|journal=Astronomy & Astrophysics|volume=538|pages=A47|year=2012|last1=Nazé|first1=Y.|last2=Rauw|first2=G.|last3=Hutsemékers|first3=D.|bibcode=2012A&A...538A..47N|arxiv = 1111.6375 |s2cid=43688343}}</ref>

Recent studies of dense clusters and mass spectrographic analysis of luminous stars have identified dozens of probable LBVs in the Milky Way out of a likely total population of just a few hundred, although few have been observed in enough detail to confirm the characteristic types of variability. In addition the majority of the LBVs in the Magellanic Clouds have been identified, several dozen in M31 and M33, plus a handful in other local group galaxies.<ref name=census>{{cite journal|bibcode=2018RNAAS...2..121R |title=The 2018 Census of Luminous Blue Variables in the Local Group |journal=Research Notes of the American Astronomical Society |volume=2 |issue=3 |pages=121 |last1=Richardson |first1=Noel D. |last2=Mehner |first2=Andrea |year=2018 |doi=10.3847/2515-5172/aad1f3|arxiv=1807.04262 |s2cid=119509358 |doi-access=free }}</ref>

[[Image:EtaCarinaeStarSystem-ChandraXRayObservatory-20140826.jpg|thumb|right|η Carinae, a luminous blue variable as seen from the Chandra X-ray Observatory]]
[[File:The star formation region Messier 17.jpg|thumb|upright=1.0|HD 168607 is the right star of the pair below the [[Astronomy:Omega Nebula|Omega Nebula]].  The other is the hypergiant HD 168625.]]
[[File:Luminous blue variable stars with Spitzer.png|thumb|right|A selection of LBVs and suspected LBVs with nebula. Observed with [[Astronomy:Spitzer Space Telescope|Spizter]].]]

=== [[Astronomy:Milky Way|Our galaxy]] ===
* [[Astronomy:Eta Carinae|η Carinae]]
* [[Astronomy:P Cygni|P Cygni]]
* [[Astronomy:AG Carinae|AG Carinae]]
* [[Astronomy:HR Carinae|HR Carinae]]
* V432 Carinae (Wray 15-751)
* [[Astronomy:HD 168607|V4029 Sagittarii]] (HD 168607)
* [[Astronomy:HD 160529|V905 Scorpii]] (HD 160529)
* V1672 Aquilae (AFGL 2298)
* [[Astronomy:Westerlund 1-243|W1-243]] (in [[Astronomy:Westerlund 1|Westerlund 1]])
* V481 Scuti (LBV G24.73+0.69)
* GCIRS 34W
* MWC 930<ref>{{cite journal|doi=10.1155/2014/130378|title=Confirmation of the Luminous Blue Variable Status of MWC 930|journal=Advances in Astronomy|volume=2014|pages=1–9|year=2014|last1=Miroshnichenko|first1=A. S.|last2=Manset|first2=N.|last3=Zharikov|first3=S. V.|last4=Zsargó|first4=J.|last5=Juárez Jiménez|first5=J. A.|last6=Groh|first6=J. H.|last7=Levato|first7=H.|last8=Grosso|first8=M.|last9=Rudy|first9=R. J.|last10=Laag|first10=E. A.|last11=Crawford|first11=K. B.|last12=Puetter|first12=R. C.|last13=Reichart|first13=D. E.|last14=Ivarsen|first14=K. M.|last15=Haislip|first15=J. B.|last16=Nysewander|first16=M. C.|last17=Lacluyze|first17=A. P.|bibcode=2014AdAst2014E...7M|arxiv = 1404.1121 |s2cid=39425211|doi-access=free}}</ref> (= V446 Scuti)
* Wray 16-137<ref>{{cite journal|bibcode=2014MNRAS.445L..84G|title=Discovery of a new Galactic bona fide luminous blue variable with Spitzer★|journal=Monthly Notices of the Royal Astronomical Society: Letters|volume=445|pages=L84–L88|last1=Gvaramadze|first1=V. V.|last2=Kniazev|first2=A. Y.|last3=Berdnikov|first3=L. N.|last4=Langer|first4=N.|last5=Grebel|first5=E. K.|last6=Bestenlehner|first6=J. M.|year=2014|doi=10.1093/mnrasl/slu141|arxiv = 1408.6232 |s2cid=41026239}}</ref>
* WS1 (discovered as [[Astronomy:Wide-field Infrared Survey Explorer|WISE]] Shell 1<ref name=wise>{{cite journal|last1=Gvaramadze|first1=V. V.|last2=Kniazev|first2=A. Y.|last3=Miroshnichenko|first3=A. S.|last4=Berdnikov|first4=L. N.|last5=Langer|first5=N.|last6=Stringfellow|first6= G. S.|last7=Todt|first7=H.|last8=Hamann|first8=W.-R.|last9=Grebel|first9=E. K.|last10=Buckley|first10=D.|last11=Crause|first11=L.|last12=Crawford|first12=S.|last13=Gulbis|first13=A.|last14=Hettlage|first14=C.|last15=Hooper|first15=E.|last16=Husser|first16=T.-O.|last17=Kotze|first17=P.|last18=Loaring|first18=N.|last19=Nordsieck|first19=K. H.|last20=O’Donoghue|first20=D.|last21=Pickering|first21=T.|last22=Potter|first22=S.|last23=Romero Colmenero|first23=E.|last24=Vaisanen|first24=P.|last25=Williams|first25=T.|last26=Wolf|first26=M.|last27=Reichart|first27=D. E.|last28=Ivarsen|first28=K. M.|last29=Haislip|first29=J. B.|last30=Nysewander|first30=M. C.|last31=LaCluyze|first31=A. P.|title=Discovery of two new Galactic candidate luminous blue variables with Wide-field Infrared Survey Explorer★|journal=Monthly Notices of the Royal Astronomical Society|volume=421|issue=4|year=2012|pages=3325–3337|issn=0035-8711|doi=10.1111/j.1365-2966.2012.20556.x|bibcode=2012MNRAS.421.3325G|arxiv = 1201.2854 |s2cid=7905464|url=http://libres.uncg.edu/ir/uncg/f/A_Miroshnichenko_Discovery_2012.pdf}}</ref>)<ref name=ws1>{{cite journal|bibcode=2015MNRAS.449L..60K|title=WS1: One more new Galactic bona fide luminous blue variable★|journal=Monthly Notices of the Royal Astronomical Society: Letters|volume=449|pages=L60–L64|last1=Kniazev|first1=A. Y.|last2=Gvaramadze|first2=V. V.|last3=Berdnikov|first3=L. N.|year=2015|doi=10.1093/mnrasl/slv023|arxiv = 1502.07361 |s2cid=119198192}}</ref>
* MN44<ref name=norma>{{cite journal|doi= 10.1093/mnras/stv2278|title= Discovery of a new bona fide luminous blue variable in Norma|journal= Monthly Notices of the Royal Astronomical Society|volume= 454|issue= 4|pages= 3710|year= 2015|last1= Gvaramadze|first1= V. V.|last2= Kniazev|first2= A. Y.|last3= Berdnikov|first3= L. N.|bibcode= 2015MNRAS.454.3710G|arxiv = 1509.08931 |s2cid= 119233401}}</ref>
* MN48<ref name=kniazev>{{cite journal|bibcode=2016MNRAS.459.3068K|title=MN48: A new Galactic bona fide luminous blue variable revealed by Spitzer and SALT★|journal=Monthly Notices of the Royal Astronomical Society|pages=stw889|last1=Kniazev|first1=A. Y.|last2=Gvaramadze|first2=V. V.|last3=Berdnikov|first3=L. N.|year=2016|doi=10.1093/mnras/stw889|arxiv = 1604.03942|volume=459|issue=3|s2cid=118616519}}</ref>
Suspected:
* [[Astronomy:G79.29+0.46|G79.29+0.46]]
* [[Astronomy:Wray 17-96|Wray 17-96]]
* [[Astronomy:HD 316285|HD 316285]]
* MN 112
* GAL 026.47+00.02
Several more LBV's have been found near or in the [[Galactic Center]]:

* [[Astronomy:V4650 Sagittarii|V4650 Sagittarii]] (FMM 362 or qF362, in the [[Astronomy:Quintuplet cluster|Quintuplet cluster]])
* [[Astronomy:V4998 Sagittarii|V4998 Sagittarii]] (LBV3, G0.120 0.048, very close to the Quintuplet cluster)
* Pistol star, Peony star and LBV 1806-20 (candidate LBV's, see below)

=== [[Astronomy:Large Magellanic Cloud|Large Magellanic Cloud]] ===
* [[Astronomy:S Doradus|S Doradus]]
* HD 269858 (= R127)
* HD 269006 (= R71)
* HD 269929 (= R143)
* HD 269662 (= R110)
* HD 269700 (= R116)<ref name="simbad">{{cite simbad|title=HD 269700|access-date=16 July 2017}}</ref>
* HD 269582 (= MWC 112)
* HD 269216<ref name=walborn>{{cite journal|bibcode=2017AJ....154...15W|title=Active Luminous Blue Variables in the Large Magellanic Cloud|journal=The Astronomical Journal|volume=154|issue=1|pages=15|last1=Walborn|first1=Nolan R.|last2=Gamen|first2=Roberto C.|last3=Morrell|first3=Nidia I.|last4=Barbá|first4=Rodolfo H.|last5=Fernández Lajús|first5=Eduardo|last6=Angeloni|first6=Rodolfo|year=2017|doi=10.3847/1538-3881/aa6195|url=http://sedici.unlp.edu.ar/handle/10915/87653|doi-access=free}}</ref>
* [[Astronomy:HD 37836|HD 37836]] (candidate)

=== [[Astronomy:Small Magellanic Cloud|Small Magellanic Cloud]] ===
* [[Astronomy:HD 5980|HD 5980]] (= R14)
* HD 6884 (= R40)

=== [[Astronomy:Andromeda Galaxy|Andromeda Galaxy]] ===
* [[Astronomy:AF Andromedae|AF Andromedae]]<ref name=m31m33>{{cite journal|doi=10.1088/0004-637X/790/1/48|title=LUMINOUS AND VARIABLE STARS IN M31 AND M33. II. LUMINOUS BLUE VARIABLES, CANDIDATE LBVs, Fe II EMISSION LINE STARS, AND OTHER SUPERGIANTS|journal=The Astrophysical Journal|volume=790|issue=1|pages=48|year=2014|last1=Humphreys|first1=Roberta M.|last2=Weis|first2=Kerstin|last3=Davidson|first3=Kris|last4=Bomans|first4=D. J.|last5=Burggraf|first5=Birgitta|bibcode=2014ApJ...790...48H|arxiv = 1407.2259 |s2cid=119177378}}</ref>
* [[Astronomy:AE Andromedae|AE Andromedae]]<ref name=m31m33/>
* Var 15<ref name=m31m33/>
* Var A-1<ref name=m31m33/>
* J004526.62+415006.3<ref name=m31new>{{cite journal|doi=10.1093/mnras/stu2597|title=New luminous blue variables in the Andromeda galaxy|journal=Monthly Notices of the Royal Astronomical Society|volume=447|issue=3|pages=2459|year=2015|last1=Sholukhova|first1=O.|last2=Bizyaev|first2=D.|last3=Fabrika|first3=S.|last4=Sarkisyan|first4=A.|last5=Malanushenko|first5=V.|last6=Valeev|first6=A.|bibcode=2015MNRAS.447.2459S|arxiv = 1412.5319 |s2cid=118374186}}</ref>
*J004051.59+403303.0<ref name=m31new/>
*LAMOST J0037+4016<ref name=lamost>{{cite journal |doi=10.3847/2041-8213/ab430b |title=A New Luminous Blue Variable in the Outskirts of the Andromeda Galaxy |journal=The Astrophysical Journal |volume=884 |issue=1 |pages=L7 |year=2019 |last1=Huang |first1=Y. |last2=Zhang |first2=H.-W. |last3=Wang |first3=C. |last4=Chen |first4=B.-Q. |last5=Zhang |first5=Y.-W. |last6=Guo |first6=J.-C. |last7=Yuan |first7=H.-B. |last8=Xiang |first8=M.-S. |last9=Tian |first9=Z.-J. |last10=Li |first10=G.-X. |last11=Liu |first11=X.-W. |bibcode=2019ApJ...884L...7H |arxiv=1909.04832 |s2cid=202558925 |doi-access=free }}</ref>

=== [[Astronomy:Triangulum Galaxy|Triangulum Galaxy]] ===
* Var 2<ref name=m31m33/> (an extremely hot star showing no variability since 1935 and hardly studied)
* [[Astronomy:Var 83|Var 83]]<ref name=m31m33/>
* [[Astronomy:List of most luminous stars|Var B]]<ref name=m31m33/>
* Var C<ref name=m31m33/>
* GR 290<ref name=maryeva>{{cite journal|bibcode=2014BaltA..23..248M|title=The half-century history of studies of Romano's star|journal=Baltic Astronomy|volume=23|issue=3–4|pages=248|last1=Maryeva|first1=Olga|year=2014|arxiv = 1411.2662 |doi=10.1515/astro-2017-0187|s2cid=118947657}}</ref> (Romano's star, an unusually hot LBV<ref name=polcaro>{{cite journal|bibcode=2016AJ....151..149P|title=GR 290 (Romano's Star): 2. Light history and evolutionary state|volume=151|issue=6|pages=149|last1=Polcaro|first1=V. F.|last2=Maryeva|first2=O.|last3=Nesci|first3=R.|last4=Calabresi|first4=M.|last5=Chieffi|first5=A.|last6=Galleti|first6=S.|last7=Gualandi|first7=R.|last8=Haver|first8=R.|last9=Mills|first9=O. F.|last10=Osborn|first10=W. H.|last11=Pasquali|first11=A.|last12=Rossi|first12=C.|last13=Vasilyeva|first13=T.|last14=Viotti|first14=R. F.|year=2016|arxiv=1603.07284|doi=10.3847/0004-6256/151/6/149|journal=The Astronomical Journal|s2cid=118409541 |doi-access=free }}</ref>)

<!-- no citation
[[Astronomy:Messier 81|M81]]:
* I1
* I2

[[Astronomy:Messier 101|M101]]:
* V1
* V2
* V10
-->
[[Astronomy:NGC 2403|NGC 2403]]:
* V12<ref name=humphreys2018>{{cite journal|doi=10.3847/1538-3881/aaf1ac|title=Luminous and Variable Stars in NGC 2403 and M81|journal=The Astronomical Journal|volume=157|pages=22|year=2018|last1=Humphreys|first1=Roberta M.|last2=Stangl|first2=Sarah|last3=Gordon|first3=Michael S.|last4=Davidson|first4=Kris|last5=Grammer|first5=Skyler H.|arxiv=1811.06559|s2cid=119379139 |doi-access=free }}</ref>
* V37<ref name=humphreys2018/>
* V38<ref name=humphreys2018/>

=== [[Astronomy:NGC 1156|NGC 1156]] ===
* J025941.21+251412.2<ref name=Solovyeva2022/>
* J025941.54+251421.8<ref name=Solovyeva2022>{{cite journal|doi=10.1093/mnras/stac3408| bibcode=2023MNRAS.518.4345S |arxiv=2208.05858 |title=Search for LBVS in the Local Volume galaxies: Study of two stars in NGC 1156 |year=2023 |last1=Solovyeva |first1=Y. |last2=Vinokurov |first2=A. |last3=Tikhonov |first3=N. |last4=Kostenkov |first4=A. |last5=Atapin |first5=K. |last6=Sarkisyan |first6=A. |last7=Moiseev |first7=A. |last8=Fabrika |first8=S. |last9=Oparin |first9=D. |last10=Valeev |first10=A. |journal=Monthly Notices of the Royal Astronomical Society |volume=518 |issue=3 |pages=4345–4356 }}</ref>

=== [[Astronomy:NGC 2366|NGC 2366]] ([[Astronomy:NGC 2363|NGC 2363]]) ===
* [[Astronomy:NGC 2363-V1|NGC 2363-V1]]

=== [[Astronomy:NGC 4449|NGC 4449]] ===
* J122809.72+440514.8<ref name=Solovyeva/>
* J122817.83+440630.8<ref name=Solovyeva>{{cite journal | doi=10.1093/mnras/stab2036 | bibcode=2021MNRAS.507.4352S | arxiv=2208.05892 | title=Search for LBVS in the Local Volume galaxies: Study of four stars in NGC 4449 | year=2021 | last1=Solovyeva | first1=Y. | last2=Vinokurov | first2=A. | last3=Sarkisyan | first3=A. | last4=Kostenkov | first4=A. | last5=Atapin | first5=K. | last6=Fabrika | first6=S. | last7=Oparin | first7=D. | last8=Valeev | first8=A. | last9=Bizyaev | first9=D. | last10=Nedialkov | first10=P. | last11=Spiridonova | first11=O. | journal=Monthly Notices of the Royal Astronomical Society | volume=507 | issue=3 | pages=4352–4366 }}</ref>

=== [[Astronomy:NGC 4736|NGC 4736]] ([[Astronomy:Messier 94|Messier 94]]) ===
* NGC 4736_1<ref>{{cite journal |doi=10.1093/mnrasl/sly241 |title=New luminous blue variable candidates in NGC 4736 |year=2019 |last1=Solovyeva |first1=Y. |last2=Vinokurov |first2=A. |last3=Fabrika |first3=S. |last4=Kostenkov |first4=A. |last5=Sholukhova |first5=O. |last6=Sarkisyan |first6=A. |last7=Valeev |first7=A. |last8=Atapin |first8=K. |last9=Spiridonova |first9=O. |last10=Moskvitin |first10=A. |last11=Nikolaeva |first11=E. |journal=Monthly Notices of the Royal Astronomical Society: Letters |volume=484 |pages=L24–L28 |arxiv=1901.05277 }}</ref>

=== [[Astronomy:PHL 293B|PHL 293B]] ===
* Unnamed star that underwent an outburst from 1998 to 2008 in an unusual supernova-like event, and has now disappeared<ref name=burke2020>{{cite journal |title=The Curious Case of PHL 293B: A Long-lived Transient in a Metal-poor Blue Compact Dwarf Galaxy |bibcode=2020ApJ...894L...5B |doi=10.3847/2041-8213/ab88de |arxiv=2002.12369 |author1=Burke, Colin J. |display-authors=0 |journal=The Astrophysical Journal Letters |volume=894 |issue=1 |date=May 2020|pages=L5 |s2cid=211572824 |doi-access=free }}</ref>

=== [[Astronomy:Sunburst galaxy|Sunburst galaxy]] ===

* [[Astronomy:Godzilla (star)|Godzilla]]

=== Other ===
A number of cLBVs in the Milky Way (and in the case of Sanduleak -69° 202, in the LMC) are well known because of their extreme luminosity or unusual characteristics, including:
* [[Astronomy:GCIRS 16SW|GCIRS 16SW]] (S97, candidate LBV orbiting the [[Astronomy:Sagittarius A*|black hole at the center of this galaxy]])
* [[Astronomy:Wray 17-96|Wray 17-96]] (unusual hypergiant in the gap between the two semi-stable LBV regions)
* [[Astronomy:Pistol Star|Pistol Star]] (once thought to be the most luminous star in the galaxy)
* [[Astronomy:LBV 1806-20|LBV 1806-20]] (one of the most luminous stars known)
* Sanduleak -69° 202 (the star that exploded as [[Astronomy:SN 1987A|SN 1987A]])
* [[Astronomy:Cygnus OB2-12|Cygnus OB2-12]] (blue [[Astronomy:Hypergiant|hypergiant]] and one of the most luminous stars known)
* HD 80077 (blue hypergiant)
* [[Astronomy:V1429 Aquilae|V1429 Aquilae]] (with a supergiant companion, very similar to a less luminous η Car)
* [[Astronomy:HD 168625|V4030 Sagittarii]] (hypergiant surrounded by a nebula identical to the one around Sanduleak -69° 202)
* [[Astronomy:WR 102ka|WR 102ka]] (the Peony star, one of the most luminous stars known, and would be one of the hottest LBVs)
* [[Astronomy:Sher 25|Sher 25]] (blue supergiant in [[Astronomy:NGC 3603|NGC 3603]] with a bipolar outflow and surrounded by a circumstellar ring)
* [[Astronomy:BD+40°4210|BD+40°4210]] (blue supergiant in the [[Astronomy:Stellar association|stellar association]] [[Astronomy:Cygnus OB2|Cygnus OB2]])

Further well-known stars have been LBVs relatively recently, are LBVs in a stable phase or are not currently classified as LBVs but may be transitioning into LBVs:{{citation needed|date=July 2020}}
* Zeta-1 Scorpii (naked-eye hypergiant)
* IRC+10420 (yellow hypergiant that has increased its temperature into the LBV range)
* [[Astronomy:V509 Cassiopeiae|V509 Cassiopeiae]] (= HR 8752, an unusual yellow hypergiant evolving bluewards)
* [[Astronomy:Rho Cassiopeiae|Rho Cassiopeiae]] (unstable yellow hypergiant suffering periodic outbursts)

==See also==
* [[Astronomy:Hypernova|Hypernova]]
* [[Astronomy:Hypergiant|Hypergiant]]

==References==
{{reflist|30em}}

==External links==
* GCVS: [http://www.sai.msu.su/groups/cluster/gcvs/cgi-bin/typ.cgi?type=SDOR List of SDOR variable stars]

{{Star}}
{{Variable star topics}}
{{supernovae}}

[[Category:Luminous blue variables| ]]
[[Category:Star types]]

{{Sourceattribution|Luminous blue variable}}