An Etymological Dictionary of Astronomy and Astrophysics

During the → main sequence stage, a star burns the hydrogen in its core and transforms it into helium. When the helium mass amounts to about 10% of the initial stellar mass, the star can no longer maintain the → hydrostatic equilibrium in its core; the star increases its volume and leaves the main sequence in order to become a → red giant.

See also: Named after the Brazilian astrophysicist Mario Schönberg (1914-1990) and Subramahmanyan Chandrasekhar, → Chandrasekhar limit, who were the first to point out this limit and derive it (1942, ApJ 96, 161).