The type of star at the end of its life cycle that has a very high density is known as a neutron star. Formed from the remnants of a supernova explosion, neutron stars are incredibly dense as their core collapses, allowing protons and electrons to combine into neutrons. This results in a star that can be just about 20 kilometers in diameter but contain a mass greater than that of the Sun. The intense gravitational forces and rapid rotation typically characterize neutron stars, often emitting detectable beams of radiation.