Low Mass Star Life

Main Sequence

Hydrogen burning in core

Subgiant

Expanding photosphere, Hydrogen burning shell around contracting inert Helium core

Red Giant

Fuse Helium in the core and burn Hydrogen in a shell.

Red Giant Branch Star

Inert Helium Core

Hydrogen burning in shell around the core.

Helium Flash

An explosion of Helium that causes core temperature to rise rapidly. Helium ash settles around the core and it contracts. Once it becomes so dense there is electron degeneracy pressure. When the core gets very hot (100 million K) the Helium rapidly begins fusion that becomes a runaway process (the reaction rate keeps increasing)

Horizontal Branch Star

Hydrogen burning shell, Helium burning core

Asymptotic Branch Star

Inert Carbon core that does not fuse because it does not reach the desired temperature (600 million Kelvin). Helium and Hydrogen burning shells.

Planetary Nebula

Ejection of all the material around the core of the star.

White Dwarf

Final form of the low mass star. It is just the carbon core and is dim and cool.