Stellar evolution
But, when a big red giant explodes, the explosion is a lot larger and is called a supernova. Instead of a white dwarf, it leaves behind a much smaller, much denser ball called a neutron star. A neutron star is created because the force of gravity is so strong that the atoms left behind would not have any electrons orbiting the nucleus of the atoms. A teaspoon of that matter might weigh as much as the entire Earth.