The final core element for a massive star is iron. Iron is the only element that can fuse and release energy in a star without producing elements heavier than iron. When a massive star runs out of hydrogen and helium to fuse, it eventually accumulates a core of iron. This core is so massive and dense that it can no longer support its own weight, and the star collapses under its own gravity. This collapse triggers a supernova, which is a powerful explosion that can release more energy than a trillion suns. The supernova scatters the star's material into space, where it can be recycled to form new stars and planets.