The Schönberg-Chandrasekhar limit is the maximum mass of a star's helium-filled core that can support the overlying layers against gravitational collapse, once the core hydrogen is exhausted; it is believed to be 10 to 15% of the total stellar mass. If this limit is exceeded, as can only happen in massive stars, the core collapses, releasing energy that causes the outer layers of the star to expand to become a red giant. It is named after Subrahmanyan Chandrasekhar and the Brazilian astrophysicist Mario Schönberg (1914–1990).