Use this tag for questions about a supernova: a massive explosion emitting light, heat and radiation that occurs when some stars die.
In a process called nuclear fusion, stars combine particles to generate power. When massive stars begin fusing heavier particles, their gravity may slowly begin to counteract the energy they put out. Eventually, too much pressure may cause a rebound, similar to hitting a rubber ball with a hammer: the hammer bounces back, and thus, the star ejects much of its material.
Alternatively, some stars go supernova when they accumulate too much matter from somewhere else, such as another nearby star.