## Wednesday, November 6, 2013

### List of most luminous stars

Below is a list of stars arranged in order of decreasing luminosity (increasing bolometric magnitude). Accurate measurement of stellar luminosities is quite difficult in practice, even when the apparent magnitude is measured accurately, for four reasons:
1. The distance d to the star must be known, to convert apparent to absolute magnitude. Absolute magnitude is the apparent magnitude a star would have if it were 10 parsecsaway from the viewer. Since apparent brightness decreases as the square of the distance (i.e. as 1/d2), a small error (e.g. 10%) in determining d implies an error ~2× as large (thus 20%) in luminosity. Stellar distances are only directly measured accurately out to d ~1000 lt-yrs.
2. The magnitudes at the wavelengths measured must be corrected for those not observed. "Absolute bolometric magnitude" (which term is redundant, practically speaking, since bolometric magnitudes are nearly always "absolute", i.e., corrected for distance) is a measure of the star's luminosity, summing over its emission at all wavelengths, and thus the total amount of energy radiated by a star every second. Bolometric magnitudes can only be estimated by correcting for unobserved portions of the spectrumthat have to be modeled, which is always an issue, and often a large correction. The list is dominated by hot blue stars which produce the majority of their energy output in the ultraviolet, but these may not necessarily be the brightest stars at visual wavelengths.
3. Even the observed magnitudes must be corrected for the absorption or extinction of intervening interstellar or circumstellar dust and gas. This correction can be enormous and difficult to determine precisely. For example, until accurate infrared observations became possible ~50 years ago, the Galactic Center region of The Milky Way was totally obscured to visual observations.
4. A large proportion of stellar systems discovered with very high luminosity have later been found to be binary. Usually this results in the total system luminosity being reduced and then that lower luminosity is spread among several components. These binaries are common both because the conditions that produce high mass high luminosity stars also favour multiple star systems, but also because searches for highly luminous stars are inevitably biased towards detecting systems with multiple more normal stars combining to appear luminous.
Because of all these problems, other references may give very different lists of the most luminous stars (different ordering or different stars altogether). Data on different stars can be of somewhat different reliability, depending on the attention one particular star has received as well as largely differing physical difficulties in analysis (see the Pistol Star for an example). The last stars in the list are familiar nearby stars put there for comparison, and not among the most luminous known. It may also interest the reader to know that the Sun is more luminous than approximately 95% of all known stars in the local neighborhood (out to, say, a few hundred light years), due to enormous numbers of somewhat less massive stars that are cooler and often much less luminous. For perspective, the overall range of stellar luminosities runs from dwarfs less than 1/10,000th as luminous as the Sun, to supergiants over 1,000,000 times more luminous.
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This list is currently limited mostly to galactic and Magellanic Cloud objects, but a few stars in other local group galaxies can now be examined in enough detail to determine the luminosities. As of mid-2012 the list is more or less complete for stars down to 1,000,000 times the luminosity of the sun. Some suspected binaries in this magnitude range are excluded because there is insufficient information about the luminosity of the individual components. Selected fainter stars are also shown for comparison.
Despite their extreme luminosity, many of these stars are nevertheless too distant to be observed with the naked eye. Stars that are at least sometimes visible to the unaided eye have their apparent magnitude (6.5 or brighter) highlighted in blue.
Star nameBolometric
luminosity
(in solar units)
Absolute
bolometric
magnitude
Approx. distance
from solar system
(in light years)
Apparent
visible magnitude
R136a1 (in LMC)8,700,000−12.6[1][2]160,00012.28
BAT99-116 (Mk34 in LMC)[a]~8,000,000−12.6[3]160,00013.10
WR 25[b]6,300,000−12.25[4]110,000~18
NGC 2363-V1[c]6,300,000−12.25[5][6]8.08
R136a2 (in LMC)6,000,000−12.2[1]160,00012.96
R136c (in LMC)5,600,000−12.1[1]160,00013.47
HD 38282 (R144 in LMC)[b][7]5,000,000−12.0[8]160,00011.15
BAT99-100 (R134 in LMC)5,000,000−12.0[3]160,00012.40
η Car[d]5,000,000[9]−12.0[9]7,500-0.8 to 7.9[10]
R136a3 (in LMC)3,800,000−11.6[1]160,00013.01
BAT99-122 (R147 in LMC)3,800,000−11.6[3]160,00012.75
Melnick 42 (in LMC)3,700,000−11.6160,00012.8
Peony Star (WR 102ka)3,200,000−11.526,100
VFTS 6823,200,000−11.5160,00016.1
LSS 40673,000,000−11.4[11]8,20011.64
NGC 3603-B2,900,000−11.3[1]24,00011.33
HD 932502,800,000−11.3[11]11,0007.50
Cygnus OB2 #8A12,750,000−11.35,0008.99
WR 102hb2,600,000[12]−11.326,000
AFGL 2298[e]2,500,000[5]−11.2533,000
HD 5980B (in SMC)2,500,000−11.25200,00011.9
WR 102ea2,500,000[12]−11.226,000
BAT99-33 (R99 in LMC)2,500,000−11.25[13]160,00011.45
WR 852,500,000−11.25[4]15,30010.03
HD 93129A[f]2,500,000−11.257,5006.97 (combined A+B)
NGC 3603-A1a2,500,000−11.2[1]24,00011.18 (combined A1a + A1b)
Var 83 (in M33)2,240,000[14]−11.13,000,00016.40
WR 1582,200,000−11.1[4]26,00011.24
Arches-F62,200,000−11.125,000
Arches-F92,200,000−11.125,000
WR 242,200,000−11.1[4]8,2006.48
HDE 269810 (in LMC)2,200,000[15]−11.1170,00012.28
Cygnus OB2 #5162,200,000−11.15000
WR 102c2,000,000[16]−11.026,000
LBV 1806-202,000,000−11.038,700
Arches-F42,000,000−11.025,000
WR 822,000,000−11.0[4]17,20011.55
WR 1312,000,000−11.0[4]38,60012.08
WR 147[g]2,000,000−11.0[4]2,10014.89
HD 5980A[h] (in SMC)2,000,000[17]−11.0200,00011.7
Arches-F72,000,000−11.025,000
Arches-F12,000,000−11.025,000
V429 Car A (=WR 22)2,000,000−11.08,2006.42
Cygnus OB2 #121,900,000−10.9[18]500011.4
Wray 17-961,800,000[19]−10.915,00017.8
V2180 Cyg (=WR 130)1,800,000−10.9[4]8,80012.14
V4650 Sgr1,800,000[20]−10.925,000
BAT99-100 (R134 in LMC)1,700,000−10.8[13]160,00012.02
BAT99110 (R136a5 in LMC)1,700,000−10.8[13]160,00013.73
Cygnus OB2-#71,700,000−10.8500012.7
Arches-F121,600,000−10.825,000
AF Andromedae (in M31)1,600,000[14]−10.82,500,000
LHO 1101,600,000[12]−10.826,000
SMC AB 8A (in SMC)1,600,000[21]−10.8200,00012.9 (combined)
V378 Vel (=WR 12)1,600,000−10.75[4]16,50010.78
The Pistol Star1,600,000−10.7525,000
WR 781,600,000−10.75[4]6,5006.49
WR 891,600,000−10.75[4]9,40011.02
WR 1071,600,000−10.75[4]13,40014.1
WR 1481,600,000−10.75[4]27,10010.3
WR 102i1,500,000[12]−10.726,000
NGC 3603-A1b1,500,000−10.6[1]24,00011.18 (combined A1a + A1b)
Arches-F151,400,000−10.625,000
V396 Carinae (=WR 16)1,400,000−10.6[4]5,0008.34
WR 1081,400,000−10.6[4]18,3009.89
WR 661,400,000−10.6[4]10,70011.34
Cygnus OB2 #7711,400,000−10.65000
R126 (in LMC)1,400,000−10.6160,00010.91
V729 Cyg A1,400,000−10.65000
Tr 27-271,350,000−10.5[11]8,200
WR 871,300,000−10.5[4]9,40011.95
WR 42e1,300,000[i]−10.5[22]25,00014.53
Arches-F31,300,000−10.525,000
Arches-F81,300,000−10.525,000
WR 1561,300,000−10.5[4]11,70011.01
BAT99-68 (in LMC)1,300,000−10.5[13]160,00012.4
BAT99-66 (in LMC)1,300,000−10.5[13]160,00015.3
R139 A (in LMC)1,300,000−10.5[23]160,00012.0 (combined)
BAT99-104 (in LMC)1,300,000−10.5[13]160,00012.5
V729 Cygni B1,300,000−10.55000
HD 500641,300,000−10.5[24]9,5008.21
WR 102d[12]1,200,000−10.426,000
V385 Carinae (=WR 40)1,100,000−10.4[4]7,4007.85
V1402 Aquilae (=WR 123)1,100,000−10.4[4]19,50011.1
Arches-F181,100,000−10.425,000
Cygnus OB2-#8B1,100,000−10.4500012.7
Cygnus OB2-#101,100,000−10.4500012.7
Cygnus OB2-#221,100,000−10.4500012.7
Var B (in M33)1,100,000[14]−10.43,000,000
BAT99-94 (R135 in LMC)1,000,000−10.3[13]160,00014.52
AG Car1,000,000[25]−10.360005.7 to 9.0
Arches-F21,000,000−10.2525,000
Arches-F141,000,000−10.2525,000
V460 Scuti (=WR 116)1,000,000−10.25[4]8,10013.38
QR Sge (=WR 124)1,000,000−10.25[4]11,00011.5
S Dor (in LMC)1,000,000−10.25169,0008.6 to 11.5 (B)
The following naked-eye stars are listed for the purpose of comparison.
P Cygni610,000−9.75,9004.8
ρ Cas550,000−9.612,0004.1 to 6.2
VY CMa450,000[26]−9.449006.5 to 9.6
ε Ori380,000−9.213001.70
ζ Pup360,000−9.010902.21
RW Cep350,000−9.1111,5006.52
μ Cep (the Garnet Star)340,000−9.0819004.04
VV Cep A315,000−9.024004.91
Plaskett's Star A224,000−8.666006.06 (A + B)
θ1 Ori C220,000−8.615005.13
Betelgeuse135,000[27][28] 6430.58
Rigel117,490−7.848600.12
Antares66,000−7.26000.92
Deneb196,000[29]−8.3826001.25
Canopus12,900−5.53310−0.62
Polaris2,200−3.64331.97
Aldebaran350−0.63650.85
Arcturus210−0.3137−0.04
Capella78.50.4420.08
Vega370.58250.00
Sirius25.41.48.6−1.46
α Centauri A1.5194.384.4−0.01
Sun1.004.83−26.74
1. Jump up^ Suspected as binary from extreme X-ray luminosty and variable radial velocity.
2.  Probable binary, with detected X-ray emission presumed to come from colliding winds. The luminosity of the individual components would obviously be less than quoted here, both because there will be multiple fainter stars, and because the combination of spectra can lead to unexpectedly high estimates of the total luminosity. Confirmed as a spectroscopic binary by Sana et al, 2013.
3. Jump up^ Luminous Blue Variable in external galaxy NGC 2363, that appears to be undergoing a "great outburst" like eta Carinae but less luminous.
4. Jump up^ Recently identified as a binary system, or possibly three stars. The secondary is also luminous at around 1,000,000 times the sun, but almost completely swamped by the primary.
5. Jump up^ Luminous Blue Variable, peak luminosity shown.
6. Jump up^ This is a known binary with two fairly similar components, but the exact details of each star are not clear. Although the luminosity of the two combined is around 2,500,000, the primary is most likely nearer 1,500,000 and the secondary about 1,000,000.
7. Jump up^ This is a binary system but the secondary is much less luminous than the primary
8. Jump up^ Variable, luminosity was five times higher at outburst in 1994.
9. Jump up^ The cited reference calculates the absolute bolometric magnitude as −10.5, then quotes a bolometric luminosity of 3.2 million times the sun which does not match. Another references estimates the luminosity directly as 1.6–3.2 million times the sun.
Note that even the most luminous stars are much less luminous than the more luminous persistent extragalactic objects, such as quasars. For example, 3C 273 has an averageapparent magnitude of 12.8 (when observing with a telescope), but an absolute magnitude of −26.7. If this object were 10 parsecs away it would appear nearly as bright in the sky as the Sun (apparent magnitude −26.74). This quasar's luminosity is, therefore, about 2 trillion (1012) times that of the Sun, or about 100 times that of the total light of average largegalaxies like our Milky Way. (Note that quasars often vary somewhat in luminosity.)
In terms of gamma rays, a magnetar (type of neutron star) called SGR 1806-20, had an extreme burst reach Earth on 27 December 2004. It was the brightest event known to have impacted this planet from an origin outside the Solar System; if these gamma rays were visible, with an absolute magnitude of approx. −29, it would be brighter than the Sun (as measured by the Swift spacecraft).
The Gamma-ray burst GRB 971214 measured in 1998 was at the time thought to be the most energetic event in the universe, with the equivalent energy of several hundredsupernovae. Later studies pointed out that the energy was probably the energy of one supernova which had been "beamed" towards Earth by the geometry of a relativistic jet.