Supernova remnant. Artwork of the wisps of gas of a supernova remnant. These thin strands of nebulosity are the remains of a star which ended its life in an enormous supernova explosion. The ejected gas may travel at thousands of kilometres per second after the explosion. The gas typically forms a loose ring-like shell around the remains of the star. After a supernova explosion, the once-massive star forms a neutron star: a tiny, extremely dense star with peculiar properties. The energy released by a supernova means that the explosion may shine as brightly as a whole galaxy of stars for a brief time.