Iron is a critical element in the understanding of how supernovas occur due to its ability to absorb energy. It is the final element produced in the nuclear reactions inside of a star and has the highest binding energy per nucleon of all elements. This means it is the most difficult element for a star to produce via nuclear fusion. Once the nuclear fusion process of star reaches iron, it can no longer absorb any more energy from the core and the star collapses under the weight of its own gravity. The resulting massive explosion of a supernova is composed of the other elements that were produced in the core of the star and the unbound iron is scattered throughout the universe. As a result, iron is critical in the understanding of how supernovas occur.
