Introductory Astronomy: Supergiants

Similar to a Red Giant , a Supergiant occurs once a massive star has used up its hydrogen in the core. It proceeds much like a red giant does, with hydrogen and then helium fusing shells, and also a helium core fusing into carbon, but it doesn't stop there. Because of the higher mass, there is now enough gravitational pressure to cause the carbon core to fuse. If the mass of the star is about 3 to 9 solar masses, the core becomes degenerate before the carbon is ignited. This causes a carbon detonation(a detonation is an explosion) which may blow the star apart, or may cause the star to go Supernova. Stars more massive than 9 solar masses will not undergo carbon detonation, and the carbon core will begin to fuse. In very massive stars, this cycle continues even further. As temperatures increase, successive layers of different fusion shells develop. The star will fuse material until it converts the core into iron. Fusing iron into another element requires more energy than it releases. Stars weren't born yesterday; they won't fuse anything that isn't to their advantage energy-wise, so fusion in the core halts once iron is produced. At this point, the star consists of an iron core (where no fusion is taking place), and shells of silicon fusion, oxygen fusion, neon fusion, carbon fusion, helium fusion, and hydrogen fusion. Because the core can no longer undergo fusion reactions, it will collapse due to gravity, and the star goes supernova.

Betelgeuse, an example of a Red Supergiant. Betelgeuse is a red supergiant, located in the constellation of Orion. Its diameter varies between 480 and 800 million miles (roughly the size of the orbit of Mars to the size of the orbit of Jupiter. At its brightest, it has a luminosity 14,000 times larger than the Sun's even though its surface temperature is only 3100 degrees Kelvin.