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.
