Stars emit light as they burn the fuel at their core, predominantly hydrogen. The heat generated from this helps the star to maintain its size. As the fuel becomes used up there is less heat, and so the star shrinks (or 'collapses'). If the star has a mass below the Chandrasekhar limit this collapse is limited by [electron degeneracy pressure]?, which results in a stable white dwarf. If the star has a mass above the Chandrasekhar limit it has sufficient gravity to collapse past the white dwarf stage and become a neutron star or black hole
The limit was calculated by the Indian phycisist [Subrahmanyan Chandrasekhar]?.