Supernova. Computer artwork of a supernova, the explosive death of a massive star. It occurs when the star runs out of fuel at the end of its life. When the nuclear reactions powering the star cease to continue, the star collapses. This is because it needs the nuclear energy to support itself against gravity, so when it is gone the star is crushed into a dense ball of matter. The density of the star is highest at its core, and when the star reaches a critical density, the outer layers rebound off the core in an enormous explosion. This explosion would engulf any planets that orbited the star, leaving them void of life.