Supernova remnant. Artwork of the glowing wisps of gas (red, green) expanding from the shining core of a supernova explosion, seen from an alien planetary system. The gas clouds were the outer layers of a massive star that ended its life in a supernova explosion. The gas expands outwards at thousands of kilometres per second, causing it to glow as it collides with the interstellar medium. Supernovae enrich this interstellar medium with the heavy elements that form in the nuclear fires at the heart of the stars. Such elements that are found on these planets will have formed in a star. The glowing clouds themselves may one day condense to form other stars and planets.