Everything about Supergiants totally explained
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've short lifespans of only 10 to 50 million years and are mainly observed in young cosmic 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, most of 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).
Further Information
Get more info on 'Supergiants'.
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