The Chandrasekhar limit is the maximum mass a white dwarf can have, about 1.4 times the mass of the Sun, derived by Subrahmanyan Chandrasekhar in 1931. Above it, the quantum pressure of electrons can no longer support the star against gravity. A white dwarf pushed past the limit by matter from a companion detonates as a type Ia supernova, the standardized explosions used to measure cosmic distances and discover dark energy.