Supernova explosion conceptual computer artwork A supernova is the explosive death of a massive star It occurs when the star runs out of fuel at the end of its life Without the nuclear reactions that powered it it can no longer support itself against gravity and it collapses When it reaches a critical density the outer layers rebound off the superdense core in an enormous explosion A supernova can outshine an entire galaxy for a few weeks Elements heavier than iron are synthesized in supernovae explosions This material is then incorporated into new generations of stars