This artists concept depicts a type of dead star called a pulsar and the surrounding disk of rubble discovered by NASAs Spitzer Space Telescope. The pulsar, called 4U 0142+61, was once a massive star until about 100,000 years ago when it blew up in a supernova explosion and scattered dusty debris into space. Some of that debris was captured into what astronomers refer to as a fall-back disk, now circling the remaining stellar core, or pulsar. The disk resembles protoplanetary disks around young stars, out of which planets are thought to be born. Supernovas are a source of iron, nitrogen and other heavy metals in the universe.