What determines how a star develops after the red giant stage in its life cycle?
1 Answer
The mass of the star determines how it develops after the red giant phase.
Explanation:
Only stars up to about 8 solar masses enter the red giant phase. This occurs when the supply of hydrogen in the star's core is depleted and the core in mainly helium. The core collapses under gravity and heats up. The hydrogen surrounding the core starts fusing and the star expands rapidly for form a red giant.
What happens next depends on the mass of the star. If the star is less than about half a solar mass, once the hydrogen supply is exhausted it will collapse into a white dwarf.
Larger stars' cores get hot enough to start helium fusion. This involves the triple alpha process which fuses helium into carbon. Once helium fusion is taking place the star stops being a red giant.
When the supply of helium is exhausted the core is mainly carbon and oxygen. Core collapse occurs but it doesn't get hot enough to start carbon fusion. The star becomes a white dwarf.
Some larger stars are able to start helium fusion in a shell around the core and then start hydrogen fusion in a shell around that. These stars enter a second red giant stage.
Ultimately all red giant stars evolve into white dwarfs with different intermediate stages depending on their mass.
