A limit concerning the evolution of stars; it states that in a star in which hydrogen has been converted to helium in the centre an inert helium core results, with there being a limit of about 10% of the mass of the star for the core. Above this limit, which is named after Mario Schoenberg (1914–90) and Subrahmanyan Chandrasekhar (1910–95), who discovered it in 1942, the core collapses and a red giant is formed.