Red supergiant

Size comparison between a red supergiant (Antares), a smaller red giant (Arcturus) and the Sun. The dashed circular curve indicates the size of the orbit of Mars.

Size comparison between a red supergiant (Antares), a smaller red giant (Arcturus) and the Sun. The dashed circular curve indicates the size of the orbit of Mars.

Red supergiants (RSGs) are supergiant stars (luminosity class I) of spectral type K or M.[1] They are the largest stars in the universe in terms of volume, although they are not the most massive. Betelgeuse and Antares are the best known red supergiants.

When a star with more than about 10 solar masses ends core hydrogen fusion, it becomes a red supergiant. A key difference to lower mass stars is that they do not undergo a helium flash in a degenerate core, but instead smoothly ignite helium in the core while continuing to fuse hydrogen in a shell. These stars have very cool surface temperatures (3500–4500 K), and enormous sizes. Some extreme examples of red supergiants are V354 Cephei, KY Cygni, and KW Sagittarii, which all have radii about 1500 times that of the Sun (about 7 astronomical units, or 7 times as far as the Earth is from the Sun). The radius of most red supergiants is between 200 and 800 times that of the Sun. They last 10 to 100 million years and are sometimes found in clusters. Luminosities can exceed 500,000 times that of the Sun. Several well-known red supergiants are:

As per their smaller kind the red giants and in contrast to Sun-like stars, instead of having a large number of small photospheric convection cells (solar granules) a red supergiant's photosphere have just a few large convective cells, whose feature cause the variations of brightness so common on both types of stars.[2]

References

  1. ↑ Henny J. G. L. M. Lamers; Joseph P. Cassinelli (17 June 1999). Introduction to Stellar Winds. Cambridge University Press. pp. 53–. ISBN 978-0-521-59565-0. Retrieved 31 August 2012.
  2. ↑ Schwarzschild, Martin (1975). "On the scale of photospheric convection in red giants and supergiants.". Astrophysical Journal 195: 137–144. Bibcode:1975ApJ...195..137S. doi:10.1086/153313.

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