When the core of a star contains essentially just iron, fusion in the core ceases. This occurs because iron is the most compact of all the elements it takes the most energy to break up the nucleus of iron than any other element . Creating heavier elements through the fusing of iron does not require a release of energy, it requires the input of energy. Because there is no energy radiating from the core, in less than 1 second, the star begins the final step in gravitational collapse. The temperature of the core goes above 100 billion degrees as the iron atoms are crushed. The intense force between the nuclei will overcome the force of gravity. The core will then recoil out from the center of the star in a massive shock wave which we observe as a supernova. When a supernova explodes it sends matter out into space at speeds up to 25,000 miles per second ( up to 40,000 kilometers per second). The blasts from supernovae produce a lot of the material in the universe. One of the materials that it produces is iron. Iron is abundant on our planet, and even in our own bodies. We all carry some type of remnant of these explosions in our own bodies. Heavy elements such as iron are created when a supernova reaches 1,000,000,000 degrees celsius. Iron and the other new elements created from the blast might appear in the new nebula that results after the explosion.