A supernova is a tremendous explosion that occurs when the core of a star exceeds the Chandrasekhar limit, and its collapse is not halted by electron degeneracy. When that happens, it takes only a fraction of a second for the stellar core to collapse into a dense ball about ten miles across. The temperature and pressure becomes almost immeasurably hot and high, and the recoil of that collapse causes an enormous detonation. More energy is released in ten seconds than the Sun will emit in its ten billion-year lifetime, as the guts of the star are blown outward into interstellar space.