Supergiant
Properties

Supergiants have masses from 8 to 12 times the Sun (M) upwards, and luminosities from about 1,000 to over a million times the Sun (L). They vary greatly in radius, usually from 30 to 500, or even in excess of 1,000 solar radii (R). They are massive enough to begin helium-core burning gently before the core becomes degenerate, without a flash and without the strong dredge-ups that lower-mass stars experience. They go on to successively ignite heavier elements, usually all the way to iron. Also because of their high masses, they are destined to explode as supernovae.

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. Radiation pressure limits the largest cool supergiants to around 1,500 R and the most massive hot supergiants to around a million L (M around − 10). Stars near and occasionally beyond these limits become unstable, pulsate, and experience rapid mass loss.
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