A giant star is a type of very large, very bright star, generally seen towards the end of a stellar lifespan. Once a subgiant star's core finally collapses into a degenerate state and the star begins dredging heavy elements to its surface, it rapidly expands. Early-stage giants fuse hydrogen in their outer shells, much like subgiants, while higher-mass giants eventually begin fusing helium into carbon and oxygen by the triple-alpha process. On an H-R diagram, the giant branch is a large ellipse near the upper right (very bright but generally cool).
Solar-mass giant stars move from the giant branch to the "red clump" or horizontal branch, and from there to the much more luminous asymptotic giant branch. Higher-mass stars generally evolve directly to supergiants.
|Stellar Luminosity Classes|
|-1 · 0 · I · II · III · IV · V · VI · VII|