Blue supergiant

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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] although sometimes A-class supergiants are also deemed blue supergiants. [2]

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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. They are most often an evolutionary phase between high-mass, hydrogen-fusing main-sequence stars and helium-fusing red supergiants, although new research suggests they could be the result of stellar mergers. [3] [4]

The majority of supergiants are also blue (B-type) supergiants; blue supergiants from classes O9.5 to B2 are even more common than their main sequence counterparts. [5]

Formation

Rigel and the IC 2118 nebula which it illuminates. Treasures3.jpg
Rigel and the IC 2118 nebula which it illuminates.

It was once believed that blue supergiants originated from a "feeding" with the interstellar medium when stars passed through interstellar dust clouds, [6] [4] although the current consensus is that blue supergiants are evolved high-mass stars, larger and more luminous than main-sequence stars. O-type and early B-type 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 (with atomic numbers of 26 (Fe) and less) 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. [7] 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 increases. [8]

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. [9] [10] 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. [11] If such a star can pass through the yellow evolutionary void it is expected that it becomes one of the lower luminosity LBVs. [12]

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. [7]

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. [13] 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. [14] 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. [15] [16] [17]

Properties

Spectrum of a B2 star. B2ii-spectra.png
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. [18]

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.[ citation needed ]

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.[ citation needed ]

Many blue supergiant stars are Alpha Cygni variables. [19]

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. [20]

Examples

Related Research Articles

<span class="mw-page-title-main">Supergiant</span> Type of star that is massive and luminous

Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram with absolute visual magnitudes between about −3 and −8. The temperature range of supergiant stars spans from about 3,400 K to over 20,000 K.

<span class="mw-page-title-main">Red supergiant</span> Stars with a supergiant luminosity class with a spectral type of K or M

Red supergiants (RSGs) are stars with a supergiant luminosity class of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelgeuse and Antares A are the brightest and best known red supergiants (RSGs), indeed the only first magnitude red supergiant stars.

<span class="mw-page-title-main">Wolf–Rayet star</span> Heterogeneous class of stars with unusual spectra

Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very high surface enhancement of heavy elements, depletion of hydrogen, and strong stellar winds. The surface temperatures of known Wolf–Rayet stars range from 20,000 K to around 210,000 K, hotter than almost all other kinds of stars. They were previously called W-type stars referring to their spectral classification.

<span class="mw-page-title-main">Deneb</span> Star in the constellation Cygnus

Deneb is a first-magnitude star in the constellation of Cygnus. Deneb is one of the vertices of the asterism known as the Summer Triangle and the "head" of the Northern Cross. It is the brightest star in Cygnus and the 19th brightest star in the night sky, with an average apparent magnitude of +1.25. A blue-white supergiant, Deneb rivals Rigel as the most luminous first-magnitude star. However, its distance, and hence luminosity, is poorly known; its luminosity is somewhere between 55,000 and 196,000 times that of the Sun. Its Bayer designation is α Cygni, which is Latinised to Alpha Cygni, abbreviated to Alpha Cyg or α Cyg.

<span class="mw-page-title-main">S Doradus</span> Star in the Large Magellanic Cloud

S Doradus is one of the brightest stars in the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way, located roughly 160,000 light-years away. The star is a luminous blue variable, and one of the most luminous stars known, having a luminosity varying widely above and below 1,000,000 times the luminosity of the Sun, although it is too far away to be seen with the naked eye.

<span class="mw-page-title-main">Luminous blue variable</span> Type of star that is luminous, blue, and variable in brightness

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 S Doradus, one of the brightest stars of the Large Magellanic Cloud. They are considered to be rare.

<span class="mw-page-title-main">Mu Cephei</span> Red supergiant star in the constellation Cepheus

Mu Cephei, also known as Herschel's Garnet Star, Erakis, or HD 206936, is a red supergiant or hypergiant star in the constellation Cepheus. It appears garnet red and is located at the edge of the IC 1396 nebula. Since 1943, the spectrum of this star has served as a spectral standard by which other stars are classified.

<span class="mw-page-title-main">P Cygni</span> Variable star in the constellation Cygnus

P Cygni is a variable star in the constellation Cygnus. The designation "P" was originally assigned by Johann Bayer in Uranometria as a nova. Located about 5,300 light-years from Earth, it is a hypergiant luminous blue variable (LBV) star of spectral type B1-2 Ia-0ep that is one of the most luminous stars in the Milky Way.

<span class="mw-page-title-main">V509 Cassiopeiae</span> Star in the constellation Cassiopeia

V509 Cassiopeiae is one of two yellow hypergiant stars found in the constellation Cassiopeia, which also contains Rho Cassiopeiae.

<span class="mw-page-title-main">Yellow hypergiant</span> Class of massive star with a spectral type of A to K

A yellow hypergiant (YHG) is a massive star with an extended atmosphere, a spectral class from A to K, and, starting with an initial mass of about 20–60 solar masses, has lost as much as half that mass. They are amongst the most visually luminous stars, with absolute magnitude (MV) around −9, but also one of the rarest, with just 20 known in the Milky Way and six of those in just a single cluster. They are sometimes referred to as cool hypergiants in comparison with O- and B-type stars, and sometimes as warm hypergiants in comparison with red supergiants.

<span class="mw-page-title-main">AG Carinae</span> Luminous variable star in the constellation Carina

AG Carinae is a star in the constellation Carina. It is classified as a luminous blue variable (LBV) and is one of the most luminous stars in the Milky Way. The great distance and intervening dust mean that the star is not usually visible to the naked eye; its apparent brightness varies erratically between magnitude 5.7 and 9.0.

<span class="mw-page-title-main">Yellow supergiant</span> Star that has a supergiant luminosity class, with a spectral type of F or G

A yellow supergiant (YSG) is a star, generally of spectral type F or G, having a supergiant luminosity class. They are stars that have evolved away from the main sequence, expanding and becoming more luminous.

<span class="mw-page-title-main">HR Carinae</span> Star in the constellation Carina

HR Carinae is a luminous blue variable star located in the constellation Carina. It is surrounded by a vast nebula of ejected nuclear-processed material because this star has a multiple shell expanding atmosphere. This star is among the most luminous stars in the Milky Way. It has very broad emission wings on the Balmer lines, reminiscent from the broad lines observed in the spectra of O and Wolf–Rayet stars. A distance of 5 kpc and a bolometric magnitude of −9.4 put HR Car among the most luminous stars of the galaxy.

<span class="mw-page-title-main">Hypergiant</span> Rare star with tremendous luminosity and high rates of mass loss by stellar winds

A hypergiant (luminosity class 0 or Ia+) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of its extreme stellar winds. The term hypergiant is defined as luminosity class 0 (zero) in the MKK system. However, this is rarely seen in literature or in published spectral classifications, except for specific well-defined groups such as the yellow hypergiants, RSG (red supergiants), or blue B(e) supergiants with emission spectra. More commonly, hypergiants are classed as Ia-0 or Ia+, but red supergiants are rarely assigned these spectral classifications. Astronomers are interested in these stars because they relate to understanding stellar evolution, especially star formation, stability, and their expected demise as supernovae.

<span class="mw-page-title-main">HD 5980</span> Triple star system in the constellation Tucana

HD 5980 is a multiple star system on the outskirts of NGC 346 in the Small Magellanic Cloud (SMC) and is one of the brightest stars in the SMC.

<span class="mw-page-title-main">O-type star</span> Stellar classification

An O-type star is a hot, blue-white star of spectral type O in the Yerkes classification system employed by astronomers. They have temperatures in excess of 30,000 kelvins (K). Stars of this type have strong absorption lines of ionised helium, strong lines of other ionised elements, and hydrogen and neutral helium lines weaker than spectral type B.

<span class="mw-page-title-main">HR 5171</span> Star in the constellation Centaurus

HR 5171, also known as V766 Centauri, is a yellow hypergiant in the constellation Centaurus. It is said to be either an extreme red supergiant (RSG) or recent post-red supergiant (Post-RSG) yellow hypergiant (YHG), both of which suggest it is one of the largest known stars. The star's diameter is uncertain but likely to be between 1,100 and 1,600 times that of the Sun, while its distance is 3.6 kpc from Earth. According to a 2014 publication, the star is a contact binary, sharing a common envelope of material with a smaller yellow supergiant and secondary star, the two orbiting each other every 1,304 ± 6 days.

<span class="mw-page-title-main">Blue loop</span> Stage of stellar evolution

In the field of stellar evolution, a blue loop is a stage in the life of an evolved star where it changes from a cool star to a hotter one before cooling again. The name derives from the shape of the evolutionary track on a Hertzsprung–Russell diagram which forms a loop towards the blue side of the diagram.

<span class="mw-page-title-main">B324</span> Star in the Triangulum Galaxy

B324 is a yellow hypergiant in the Triangulum Galaxy, located near the giant H II region IC 142 around 2.7 million light years away. It is the brightest star in the Triangulum Galaxy in terms of apparent magnitude.

References

  1. ↑ 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.
  2. 1 2 3 Yüce, Kutluay (2005-01-01). "Spectral Analysis of 4 Lacertae and ν Cephei". Baltic Astronomy. 14: 51–82. Bibcode:2005BaltA..14...51Y. ISSN   1021-6766.
  3. ↑ Menon, Athira; Ercolino, Andrea; Urbaneja, Miguel A.; Lennon, Daniel J.; Herrero, Artemio; Hirai, Ryosuke; Langer, Norbert; Schootemeijer, Abel; Chatzopoulos, Emmanouil; Frank, Juhan; Shiber, Sagiv (March 2024). "Evidence for Evolved Stellar Binary Mergers in Observed B-type Blue Supergiants". The Astrophysical Journal Letters. 963 (2): L42. Bibcode:2024ApJ...963L..42M. doi: 10.3847/2041-8213/ad2074 . ISSN   2041-8205.
  4. 1 2 Koberlein, Brian (2024-03-26). "Merging Stars Can Lead to Blue Supergiants". Universe Today. Retrieved 2024-03-28.
  5. ↑ Sowell, J. R.; Trippe, M.; Caballero-Nieves, S. M.; Houk, N. (2007-07-18). "H-R Diagrams Based on the HD Stars in the Michigan Spectral Catalogue and the Hipparcos Catalog". The Astronomical Journal. 134 (3): 1089. Bibcode:2007AJ....134.1089S. doi:10.1086/520060. ISSN   1538-3881.
  6. ↑ Galaxy v23n06 (1965 08).
  7. 1 2 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.
  8. ↑ Eggenberger, P.; Meynet, G.; Maeder, A. (2009). "Modelling massive stars with mass loss". Communications in Asteroseismology. 158: 87. Bibcode:2009CoAst.158...87E.
  9. ↑ 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.
  10. ↑ 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.
  11. ↑ 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.
  12. ↑ 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 .
  13. ↑ 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. Vol. 937. pp. 163–170. arXiv: 0705.3066 . doi:10.1063/1.2803557. S2CID   18799766.{{cite book}}: |journal= ignored (help)
  14. ↑ 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.
  15. ↑ 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.
  16. ↑ 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.
  17. ↑ Georgy, C. (2012). "Yellow supergiants as supernova progenitors: An indication of strong mass loss for red supergiants?". Astronomy & Astrophysics. 538: L8–L2. arXiv: 1111.7003 . Bibcode:2012A&A...538L...8G. doi:10.1051/0004-6361/201118372. S2CID   55001976.
  18. ↑ 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.
  19. ↑ Saio, H.; Georgy, C.; Meynet, G. (2013). "Strange-Mode Instability for Micro-Variations in Luminous Blue Variables". Progress in Physics of the Sun and Stars: A New Era in Helio- and Asteroseismology. Proceedings of a Fujihara Seminar held 25–29 November. Astronomical Society of the Pacific Conference Series. Vol. 479. p. 47. arXiv: 1305.4728 . Bibcode:2013ASPC..479...47S.
  20. ↑ 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.
  21. ↑ "Deneb | Blue Supergiant, Cygnus Constellation & Alpha Cygni | Britannica". www.britannica.com. Retrieved 2024-03-19.
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