A supergiant star is a type of extremely large, very luminous star, that is generally near the end of its lifespan. Once a massive star's core collapses into a degenerate state after burning out its hydrogen and the star begins burning heavier elements to its surface, it rapidly expands and loses mass, becoming a red supergiant, which can be hundreds to thousands of times the radius of our sun. On an H-R diagram, supergiants make up the near top (very bright, but very cool).

Supergiants are of luminosity class I; however, there are generally considered three subdivisions:

  • Ia: bright supergiants
  • Iab: supergiants of intermediate brightness
  • Ib: less-bright supergiants

Supergiants go out via supernova, an extremely powerful explosion that occurs when the core can no longer support itself due to gravity. If the core had exceeded the Chandrasekhar limit at about 1.5 solar masses, the result of the supernova would be a neutron star. If it exceeded the Tolman–Oppenheimer–Volkoff limit at 3 solar masses, the star would turn into a black hole.


Stellar Luminosity Classes
-1 · 0 · I · II · III · IV · V · VI · VII
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