Supergiant


Supergiant

Supergiants are among the most massive stars. In the Hertzsprung-Russell diagram they occupy the top region of the diagram. In the Yerkes spectral classification supergiants are class Ia (most luminous supergiants) or Ib (less luminous supergiants). They typically have bolometric absolute magnitudes between -5 and -12. The most luminous supergiants are often classified as hypergiants of class 0.

Supergiants can have masses from 10 to 70 solar masses and brightness from 30,000 up to hundreds of thousands times the solar luminosity. They vary greatly in radii, usually from 30 to 500, or even in excess of 1000 solar radii. The Stefan-Boltzmann law dictates that the relatively cool surfaces of red supergiants radiate much less energy per unit area than those of blue supergiants; thus, for a given luminosity red supergiants are larger than their blue counterparts.

Because of their extreme masses they have short lifespans of 30 million years down to a few hundred thousand years (by the equation "M" - 2.5 × 1010 where "M" = mass in sols) [cite web
last = Richmond | first = Michael
url = http://spiff.rit.edu/classes/phys230/lectures/star_age/star_age.html
title = Stellar evolution on the main sequence
accessdate = 2006-08-24
] . They are mainly observed in young galactic structures such as open clusters, the arms of spiral galaxies, and in irregular galaxies. They are less abundant in spiral galaxy bulges, and are rarely observed in elliptical galaxies, or globular clusters, which are believed to be composed of old stars.

Supergiants occur in every spectral class from young blue class O supergiants stars to highly evolved red class M supergiants. Rigel, the brightest star in the constellation Orion is a typical blue-white supergiant, whereas Betelgeuse and Antares are red supergiants.

The modelling of supergiants is still an active area of research and is made more difficult by issues such as stellar mass loss. Rather than modelling individual stars, the latest trend has been to model clusters of stars and then compare the distribution of the resulting models with the observed supergiant distributions in galaxies like the Magellanic Clouds.

The first stars in the universe are thought to have been considerably brighter and more massive than the stars in the modern universe. These stars were part of the theorized population III of stars. Their existence is necessary to explain observations of elements other than hydrogen and helium in quasars.

Most type II supernova progenitors are thought to be red supergiants. However, the progenitor for Supernova 1987A was a blue supergiant. It is believed that it was a red supergiant before losing its outer layers to its strong stellar wind.

Currently, the largest known stars in terms of physical size, not mass, brightness or luminosity, are the supergiants VY Canis Majoris, VV Cephei, V354 Cephei, KW Sagitarii, KY Cygni, and μ Cephei (the Garnet Star).

ee also

*Giant star
*Red giant
*Red supergiant
*Blue supergiant
*Hypergiants
*List of stellar angular diameters

References

*cite book|first=Piero (editor)|last=Tempesti|title=Enciclopedia dell'Astronomia|publisher=Curcio|year=1979


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Look at other dictionaries:

  • supergiant — [so͞o′pər jī΄ənt] n. an immense and extremely luminous star, as Betelgeuse or Antares, that has a diameter at least 100 times that of the sun and that is 100 to more than 10,000 times as bright …   English World dictionary

  • supergiant — noun Date: 1926 something that is extremely large; especially a star of very great intrinsic luminosity and enormous size • supergiant adjective …   New Collegiate Dictionary

  • supergiant — /sooh peuhr juy euhnt/, n. 1. Astron. See supergiant star. 2. an extremely large or powerful person, company, thing, etc. adj. 3. extremely large; immense. [1925 30; SUPER + GIANT] * * * …   Universalium

  • supergiant — noun A very large star having a mass between 10 and 70 solar masses …   Wiktionary

  • supergiant — adj. especially bright star whose diameter is 100 times larger than that of the sun (Astronomy) …   English contemporary dictionary

  • supergiant — noun Astronomy a star that is greater and more luminous than a giant …   English new terms dictionary

  • supergiant — su·per·giant …   English syllables

  • supergiant — su•per•gi•ant [[t]ˈsu pərˌdʒaɪ ənt[/t]] n. astron. a very bright, very large star, hundreds of times larger than the sun • Etymology: 1925–30 …   From formal English to slang

  • supergiant — /ˈsupədʒaɪənt/ (say soohpuhjuyuhnt) noun any of a number of very large, highly luminous, low density stars, as Betelgeuse or Antares …   Australian English dictionary

  • Supergiant —    The largest type of Red Stars. These stars have diameters over 400 times larger than that of our Sun, but they are not very dense, maybe only 40 times more than our Sun …   The writer's dictionary of science fiction, fantasy, horror and mythology


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