Red Giant

From Galactic Patrol Wiki

Red Giant

A Red Giant is a luminous giant star of low or intermediate mass that is in a later phase of its evolution, with nuclear fusion going on in a shell outside the core but not in the core itself. The core matter is electron degenerate and extremely compressed, so the outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower. The appearance of the red giant is from yellow orange to red, including the spectral types K and M, but also class S stars and most carbon stars.

The most common red giants are the so-called Red Giant Branch stars (RGB stars) whose shells are still fusing hydrogen, while the core is inactive helium. Another case of red giants of interest are the Asymptotic Giant Branch stars (AGB) that produces carbon by the triple-alpha process from helium. To the AGB stars belong the carbon stars of type C-N and late C-R.

Prominent bright red giants in the Milky Way Galaxy include Aldebaran (Alpha Tauri), Gamma Crucis and Alpha Vulpeculae (Lucida Anseris).