Supernova explosion
A supernova explosion, one of the major cataclysm of the universe, is a rare event at the scale of a galaxy. It sows in the intergalactic space elements heavier than iron, that will contribute later in to the formation of stars and planets. Two of these heavy éléments, thorium and uranium, which are radioactive have survived due to very long lifetimes. This photo of a very early event in universe was taken in 1996 on board of the ISO satellite.