A pair-instability supernova is a type of supernova predicted to occur when pair production — the production of free electrons and positrons in the collision between atomic nuclei and energetic gamma rays — temporarily reduces the internal radiation pressure supporting a supermassive star's core against gravitational collapse. This pressure drop leads to a partial collapse, which in turn causes greatly accelerated burning in a runaway thermonuclear explosion, resulting in the star being blown completely apart without leaving a stellar remnant behind.