Neutron Stars

If a star is a high mass star with a mass above 5 solar masses, it doesn't form a white dwarf when it dies. These stars end their lives much more violently. Instead, the star dies in a catastrophic supernova explosion, and the remaining core becomes a neutron star. In the final stages of their lives, they proceed to fuse increasingly heavier elements until they have exhausted all possible fusion sources. When fusion ceases, gravity drives the core to implode, resulting in a titanic supernova explosion, leaving behind a neutron star. As its name implies, a neutron star is an exotic type of star that is composed entirely of neutrons. This is because the intense gravity of the neutron star crushes protons and electrons together to form neutrons.
Examples of supernova remnants are Vela, Crab Nebula, Veil Nebula and Supernova 1987A. If stars are even more massive, they will become black holes instead of neutron stars after the supernova goes off.