Supernova explosion computer artwork. A supernova is the result of a massive star exhausting the hydrogen and helium that fuel its nuclear fires. It is the heat from these nuclear fusion processes that prevents the star collapsing under its own weight. Further nuclear fusion involving other elements is less efficient and destabilises the star. In less than one second, the core collapses under its own weight. A rebounding shock wave from the super-dense core blows off the outer layers of the star (as seen) at thousands of kilometres per second. A supernova may briefly outshine an entire galaxy. A massive core may continue to collapse, forming a black hole and warping space-time.