In the formation of a supernova, all the hydrogen is used up and a given star undergoes a sudden increase in brightness, with variations that can reach 19 magnitudes (about 100 times brighter than an ordinary nova). The glow caused by the explosion of a supernova can take weeks or even months to disappear. Supernovae represent the beginning of the final phase of evolution of massive stars.

The explosion results from uncontrolled thermonuclear reactions that occur inside these stars, as a result of which matter is launched into space at great speeds. In this explosion, up to 90% of the star can be thrown into space. The remaining mass appears in the form of an expanding gas cloud and possibly a compact stellar object, which could be a neutron star or a black hole.