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(soo -per-jÿ-ănt) The largest and most luminous type of star, lying above both the main sequence and the giant region in the Hertzsprung–Russell diagram. They are grouped in luminosity classes Ia and Ib (see spectral types) and generally have absolute bolometric magnitudes between –5 and –12. Only the most massive stars can become supergiants and consequently they are very rare. They are so bright, however, that they stand out in external galaxies. There is an upper limit to the absolute bolometric magnitude of cool red supergiants (–9.7), so the brightest supergiants can be used as approximate distance indicators. Examples of supergiant stars are Rigel and Betelgeuse in Orion, Antares in Scorpius, and Cepheid variable stars. See also luminous blue variables.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



in astronomy, a massive star of the highest luminosity. The absolute stellar magnitudes of supergiants reach values of - 7 and - 8. Supergiants include stars of various spectral classes. The diameters of cool (red) supergiants, such as Betelgeuse or the red component of VV Cephei, are hundreds or thousands of times greater than the diameter of the sun. The diameters of hot supergiants, such as Rigel, exceed the diameter of the sun by a factor of 20 to 30. The total fraction of supergiants among all the stars is small. Supergiants occur in stellar associations and in younger open clusters; they often are components of binary systems. Observations indicate an escape of matter from the surface of many supergiants as well as other signs of instability. All such phenomena make the supergiants particularly important for the development of a theory of stellar evolution.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The size of these "bubbles" is also gigantic, as large as the supergiant star itself.
But, some massive stars become red supergiant stars first, which is an intermediate phase where, after the fuel in the centre is used up, energy is still produced in shells surrounding the now dead core.
This time intensive method establishes that it was these two red supergiant stars that produced the supernovae 2003J and 2003gd, and confirms that red supergiant stars create type II supernovae.
While low-mass dwarf stars like the Sun keep most products of their reactions locked up inside like old misers, high-mass supergiant stars spread the wealth like philanthropists in self-obliterating explosions known as supernovae.
This time the Moon will cross not a big planet but big Antares, one of the two brightest red supergiant stars in the sky (the other being Betelgeuse, which is too far from the ecliptic for the Moon ever to occult it).
Now Vlemmings, Philip Diamond (Jodrell Bank Observatory), and Huib Jan van Langevelde (Joint Institute for VLBI in Europe) have used the Very Long Baseline Array to study water masers in the stellar winds of three supergiant stars (S Persei, VY Canis Majoris, and NML Cygni) and one Mira variable (U Herculis).
The first unit, named Antu (at left below), is already providing very high-resolution images such as this one resolving many blue supergiant stars in the spiral galaxy M83.
They found two possible scenarios that resulted in red-giant and supergiant stars being torn apart.
However, this doesn't mean they are massive supergiant stars, as a strict interpretation of the "rules" would imply.
Astronomers used to think a high-mass supergiant star was needed to account for the brightness of Epsilon Aurigae despite its great distance.