A blue supergiant (BSG) is a hot, luminous star, often referred to as an OB supergiant. They have luminosity class I and spectral class B9 or earlier.[1]
Blue supergiants are found towards the top left of the Hertzsprung–Russell diagram, above and to the right of the main sequence. They are larger than the Sun but smaller than a red supergiant, with surface temperatures of 10,000–50,000 K and luminosities from about 10,000 to a million times that of the Sun.
Formation
Rigel and the IC 2118 nebula which it illuminates.
Supergiants are evolved high-mass stars, larger and more luminous than main-sequence stars. O class and early B class stars with initial masses around 10–300 M☉ evolve away from the main sequence in just a few million years as their hydrogen is consumed and heavy elements start to appear near the surface of the star. These stars usually become blue supergiants, although it is possible that some of them evolve directly to Wolf–Rayet stars.[2] Expansion into the supergiant stage occurs when hydrogen in the core of the star is depleted and hydrogen shell burning starts, but it may also be caused as heavy elements are dredged up to the surface by convection and mass loss due to radiation pressure increase.[3]
Blue supergiants are newly evolved from the main sequence, have extremely high luminosities, high mass loss rates, and are generally unstable. Many of them become luminous blue variables (LBVs) with episodes of extreme mass loss. Lower mass blue supergiants continue to expand until they become red supergiants. In the process they must spend some time as yellow supergiants or yellow hypergiants, but this expansion occurs in just a few thousand years and so these stars are rare. Higher mass red supergiants blow away their outer atmospheres and evolve back to blue supergiants, and possibly onwards to Wolf–Rayet stars.[4][5] Depending on the exact mass and composition of a red supergiant, it can execute a number of blue loops before either exploding as a type II supernova or finally dumping enough of its outer layers to become a blue supergiant again, less luminous than the first time but more unstable.[6] If such a star can pass through the yellow evolutionary void it is expected that it becomes one of the lower luminosity LBVs.[7]
The most massive blue supergiants are too luminous to retain an extensive atmosphere and they never expand into a red supergiant. The dividing line is approximately 40 M☉, although the coolest and largest red supergiants develop from stars with initial masses of 15–25 M☉. It is not clear whether more massive blue supergiants can lose enough mass to evolve safely into old age as a Wolf Rayet star and finally a white dwarf, or they reach the Wolf Rayet stage and explode as supernovae, or they explode as supernovae while blue supergiants.[2]
Supernova progenitors are most commonly red supergiants and it was believed that only red supergiants could explode as supernovae. SN 1987A, however, forced astronomers to re-examine this theory, as its progenitor, Sanduleak -69° 202, was a B3 blue supergiant.[8] Now it is known from observation that almost any class of evolved high-mass star, including blue and yellow supergiants, can explode as a supernova although theory still struggles to explain how in detail.[9] While most supernovae are of the relatively homogeneous type II-P and are produced by red supergiants, blue supergiants are observed to produce supernovae with a wide range of luminosities, durations, and spectral types, sometimes sub-luminous like SN 1987A, sometimes super-luminous such as many type IIn supernovae.[10][11][12]
Properties
Spectrum of a B2 star.
Because of their extreme masses they have relatively short lifespans and are mainly observed in young cosmic structures such as open clusters, the arms of spiral galaxies, and in irregular galaxies. They are rarely observed in spiral galaxy cores, elliptical galaxies, or globular clusters, most of which are believed to be composed of older stars, although the core of the Milky Way has recently been found to be home to several massive open clusters and associated young hot stars.[13]
The best known example is Rigel, the brightest star in the constellation of Orion. Its mass is about 20 times that of the Sun, and its luminosity is around 117,000 times greater. Despite their rarity and their short lives they are heavily represented among the stars visible to the naked eye; their immense brightness is more than enough to compensate for their scarcity.
Blue supergiants have fast stellar winds and the most luminous, called hypergiants, have spectra dominated by emission lines that indicate strong continuum driven mass loss. Blue supergiants show varying quantities of heavy elements in their spectra, depending on their age and the efficiency with which the products of nucleosynthesis in the core are convected up to the surface. Quickly rotating supergiants can be highly mixed and show high proportions of helium and even heavier elements while still burning hydrogen at the core; these stars show spectra very similar to a Wolf Rayet star.
While the stellar wind from a red supergiant is dense and slow, the wind from a blue supergiant is fast but sparse. When a red supergiant becomes a blue supergiant, the faster wind it produces impacts the already emitted slow wind and causes the outflowing material to condense into a thin shell. In some cases several concentric faint shells can be seen from successive episodes of mass loss, either previous blue loops from the red supergiant stage, or eruptions such as LBV outbursts.[14]
Examples
MACS J1149 Lensed Star 1 (or Icarus) – most distant individual star detected
Rigel (β Orionis), a blue-white (B-type) supergiant
UW Canis Majoris (UW CMa), a blue (O-type) supergiant
Zeta Puppis (Naos), a blue (O-type) supergiant
References
Massey, P.; Puls, J.; Pauldrach, A. W. A.; Bresolin, F.; Kudritzki, R. P.; Simon, T. (2005). "The Physical Properties and Effective Temperature Scale of O‐Type Stars as a Function of Metallicity. II. Analysis of 20 More Magellanic Cloud Stars and Results from the Complete Sample". The Astrophysical Journal. 627 (1): 477–519. arXiv:astro-ph/0503464. Bibcode:2005ApJ...627..477M. doi:10.1086/430417. S2CID 18172086.
Georges Meynet; Cyril Georgy; Raphael Hirschi; Andre Maeder; Phil Massey; Norbert Przybilla; Fernanda Nieva (2011). "Red Supergiants, Luminous Blue Variables and Wolf-Rayet stars: The single massive star perspective". Bulletin de la Société Royale des Sciences de Liège. 80 (39): 266–278. arXiv:1101.5873. Bibcode:2011BSRSL..80..266M.
Eggenberger, P.; Meynet, G.; Maeder, A. (2009). "Modelling massive stars with mass loss". Communications in Asteroseismology. 158: 87. Bibcode:2009CoAst.158...87E.
Origlia, L.; Goldader, J. D.; Leitherer, C.; Schaerer, D.; Oliva, E. (1999). "Evolutionary Synthesis Modeling of Red Supergiant Features in the Near‐Infrared". The Astrophysical Journal. 514 (1): 96–108. arXiv:astro-ph/9810017. Bibcode:1999ApJ...514...96O. doi:10.1086/306937. S2CID 14757900.
Neugent; Philip Massey; Brian Skiff; Georges Meynet (2012). "Yellow and Red Supergiants in the Large Magellanic Cloud". The Astrophysical Journal. 749 (2): 177. arXiv:1202.4225. Bibcode:2012ApJ...749..177N. doi:10.1088/0004-637X/749/2/177. S2CID 119180846.
Maeder, A.; Meynet, G. (2001). "Stellar evolution with rotation. VII". Astronomy and Astrophysics. 373 (2): 555–571. arXiv:astro-ph/0105051. Bibcode:2001A&A...373..555M. doi:10.1051/0004-6361:20010596. S2CID 18125436.
Stothers, R. B.; Chin, C. W. (2001). "Yellow Hypergiants as Dynamically Unstable Post–Red Supergiant Stars". The Astrophysical Journal. 560 (2): 934. Bibcode:2001ApJ...560..934S. doi:10.1086/322438. hdl:2060/20010083764.
Smith, N.; Immler, S.; Weiler, K. (2007). "Galactic Twins of the Nebula Around SN 1987A: Hints that LBVS may be supernova progenitors". AIP Conference Proceedings. 937. pp. 163–170. arXiv:0705.3066. doi:10.1063/1.2803557. S2CID 18799766.
Gal-Yam, A.; Leonard, D. C. (2009). "A Massive Hypergiant Star as the Progenitor of the Supernova SN 2005gl" (PDF). Nature. 458 (7240): 865–867. Bibcode:2009Natur.458..865G. doi:10.1038/nature07934. PMID 19305392. S2CID 4392537. Archived from the original (PDF) on 2016-03-03. Retrieved 2015-08-28.
Mauerhan; Nathan Smith; Alexei Filippenko; Kyle Blanchard; Peter Blanchard; Casper; Bradley Cenko; Clubb; Daniel Cohen (2012). "The Unprecedented Third Outburst of SN 2009ip: A Luminous Blue Variable Becomes a Supernova". American Astronomical Society Meeting Abstracts #221. 221: 233.03. arXiv:1209.6320. Bibcode:2013AAS...22123303M. doi:10.1093/mnras/stt009. S2CID 119087896.
Kleiser, I.; Poznanski, D.; Kasen, D.; et al. (2011). "The Peculiar Type II Supernova 2000cb". Bulletin of the American Astronomical Society. 43: 33726. Bibcode:2011AAS...21733726K.
Georgy, C. (2012). "Yellow supergiants as supernova progenitors: An indication of strong mass loss for red supergiants?". Astronomy and Astrophysics. 538: L8–L2. arXiv:1111.7003. Bibcode:2012A&A...538L...8G. doi:10.1051/0004-6361/201118372. S2CID 55001976.
Figer, D. F.; Kim, S. S.; Morris, M.; Serabyn, E.; Rich, R. M.; McLean, I. S. (1999). "Hubble Space Telescope/NICMOS Observations of Massive Stellar Clusters near the Galactic Center" (PDF). The Astrophysical Journal. 525 (2): 750. arXiv:astro-ph/9906299. Bibcode:1999ApJ...525..750F. doi:10.1086/307937. S2CID 16833191.
Chiţǎ, S. M.; Langer, N.; Van Marle, A. J.; García-Segura, G.; Heger, A. (2008). "Multiple ring nebulae around blue supergiants". Astronomy and Astrophysics. 488 (2): L37. arXiv:0807.3049. Bibcode:2008A&A...488L..37C. doi:10.1051/0004-6361:200810087. S2CID 58896016.
vte
Accretion Molecular cloud Bok globule Young stellar object
Protostar Pre-main-sequence Herbig Ae/Be T Tauri FU Orionis Herbig–Haro object Hayashi track Henyey track
Main sequence Red-giant branch Horizontal branch
Red clump Asymptotic giant branch
super-AGB Blue loop Protoplanetary nebula Planetary nebula PG1159 Dredge-up OH/IR Instability strip Luminous blue variable Blue straggler Stellar population Supernova Superluminous supernova / Hypernova
Early Late Main sequence
O B A F G K M Brown dwarf WR OB Subdwarf
O B Subgiant Giant
Blue Red Yellow Bright giant Supergiant
Blue Red Yellow Hypergiant
Yellow Carbon
S CN CH White dwarf Chemically peculiar
Am Ap/Bp HgMn Helium-weak Barium Extreme helium Lambda Boötis Lead Technetium Be
Shell B[e]
White dwarf
Helium planet Black dwarf Neutron
Radio-quiet Pulsar
Binary X-ray Magnetar Stellar black hole X-ray binary
Burster
Hypothetical
Blue dwarf Green Black dwarf Exotic
Boson Electroweak Strange Preon Planck Dark Dark-energy Quark Q Black Gravastar Frozen Quasi-star Thorne–Żytkow object Iron Blitzar
Deuterium burning Lithium burning Proton–proton chain CNO cycle Helium flash Triple-alpha process Alpha process Carbon burning Neon burning Oxygen burning Silicon burning S-process R-process Fusor Nova
Symbiotic Remnant Luminous red nova
Structure
Core Convection zone
Microturbulence Oscillations Radiation zone Atmosphere
Photosphere Starspot Chromosphere Stellar corona Stellar wind
Bubble Bipolar outflow Accretion disk Asteroseismology
Helioseismology Eddington luminosity Kelvin–Helmholtz mechanism
Properties
Designation Dynamics Effective temperature Luminosity Kinematics Magnetic field Absolute magnitude Mass Metallicity Rotation Starlight Variable Photometric system Color index Hertzsprung–Russell diagram Color–color diagram
Star systems
Binary
Contact Common envelope Eclipsing Symbiotic Multiple Cluster
Open Globular Super Planetary system
Earth-centric
observations
Sun
Solar System Sunlight Pole star Circumpolar Constellation Asterism Magnitude
Apparent Extinction Photographic Radial velocity Proper motion Parallax Photometric-standard
Lists
Proper names
Arabic Chinese Extremes Most massive Highest temperature Lowest temperature Largest volume Smallest volume Brightest
Historical Most luminous Nearest
Nearest bright With exoplanets Brown dwarfs White dwarfs Milky Way novae Supernovae
Candidates Remnants Planetary nebulae Timeline of stellar astronomy
Related articles
Substellar object
Brown dwarf Sub-brown dwarf Planet Galactic year Galaxy Guest Gravity Intergalactic Planet-hosting stars Tidal disruption event
vte
Supernovae
Classes
Type Ia Type Ib and Ic Type II (IIP, IIL, IIn, and IIb) Hypernova Superluminous Pair-instability
Physics of
Calcium-rich Carbon detonation Foe Near-Earth Phillips relationship Nucleosynthesis
P-process R-process Neutrinos
Related
Imposter
pulsational pair-instability Failed Gamma-ray burst Kilonova Luminous red nova Nova Pulsar kick Quark-nova Symbiotic nova
Progenitors
Hypergiant
yellow Luminous blue variable Supergiant
blue red yellow White dwarf
related links Wolf–Rayet star
Remnants
Supernova remnant
Pulsar wind nebula Neutron star
pulsar magnetar related links Stellar black hole
related links Compact star
quark star exotic star Zombie star Local Bubble Superbubble
Orion–Eridanus
Discovery
Guest star History of supernova observation Timeline of white dwarfs, neutron stars, and supernovae
Lists
Candidates Notable Massive stars Most distant Remnants In fiction
Notable
Barnard's Loop Cassiopeia A Crab
Crab Nebula iPTF14hls Tycho's Kepler's SN 1987A SN 185 SN 1006 SN 2003fg Remnant G1.9+0.3 SN 2007bi SN 2011fe SN 2014J SN Refsdal Vela Remnant
Research
ASAS-SN Calán/Tololo Survey High-Z Supernova Search Team Katzman Automatic Imaging Telescope Monte Agliale Supernovae and Asteroid Survey Nearby Supernova Factory Sloan Supernova Survey Supernova/Acceleration Probe Supernova Cosmology Project SuperNova Early Warning System Supernova Legacy Survey Texas Supernova Search
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