A supernova is the spectacular explosion of a high-mass star that has come to the end of its life. For a brief time, a supernova can shine as brightly as an entire galaxy, but will fade again over a matter of days.
The explosion occurs when a high-mass star finally runs out of nuclear fuel. Without any outward pressure to balance the inward force of gravity, the outer layers of the star collapse onto the core, and are then dramatically expelled in a nuclear explosion, at a velocity of up to 30,000 km/s. The resulting shock wave creates an expanding shell of gas and dust called a supernova remnant.
After many millions of years, the material in the supernova remnant will be scattered into nearby gas clouds and may eventually be used in the birth of a new star. The majority of elements in the universe were created by nuclear reactions at the centre of stars. It is safe to say that we are all made from the stardust of long-dead stars.