Evolution of a Solar-Mass Star off the Main Sequence
Red Giant Branch (RGB)
The Helium Flash and Triple Alpha Process
Horizontal Branch (HB)
Asymptotic Giant Branch (AGB)
Evolutionary Tracks
Evolution of High-Mass Stars Post-Main Sequence
Evolution of Low-Mass Stars Post-Main Sequence
Eventually the core exhausts its supply of hydrogen and the star begins to evolve off of the main sequence. Without the outward pressure generated by the fusion of hydrogen to counteract the force of gravity the core contracts until either electron degeneracy pressure becomes sufficient to oppose gravity or the core becomes hot enough (around 100 MK) for helium fusion to begin. Which of these happens first depends upon the star's mass.