In the most common case, the innermost part of a large star (called the core) stops burning and without this source of heat, the forces holding electrons and protons apart are no longer strong enough to do so. The core collapses in on itself exceedingly quickly, and becomes a neutron star or black hole ; the outer layers of the original star fall inwards and may rebound off the newly created neutron star (if one was created), creating a supernova.