V A Supernovas occur at the end of a stars lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy. When the star explodes its core collapses and in doing so releases a huge amount of energy. The cores can not generate energy.
Some supernovas are so bright that it can easily be seen throughout the universe.
The explosions give out an enormous amounts of gas and dust into space. The mass of dust and gas can exceed the mass of the sun by 10 times. Most supernovae reach maximum brightness a few days after they explode. In those first few days, the supernova emits as much energy as a whole galaxy. Supernovae can shine intensely for several weeks.