A supernova is an Earth term for a stellar explosion, far more energetic than a nova that expels most, if not all of a star's matter at roughly 1/10 the speed of light, sometimes leaving behind a dense remnant that becomes a neutron star or collapses into a black hole. Such an explosion will cause the star's luminosity to increase by as much as 20 magnitudes, briefly outshining whole galaxies before fading. The phenomena can be caused either by a gravitational collapse at the end of a star's life, or by a massive accretion of hydrogen from a stellar neighbour onto a white dwarf, resulting in a runaway nuclear fusion reaction. An especially bright or energetic supernova is called a hypernova.
- Supernova on Wikipedia.