Neutron stars, any of a class of extremely dense, compact stars thought to be composed primarily of neutrons.
Neutron stars are formed when a massive star runs out of fuel and collapses.
Neutron Stars are typically about 20 km (12 miles) in diameter.
Their masses range between 1.18 and 1.97 times that of the Sun.
But most are 1.35 times that of the Sun.
Thus, their mean densities are extremely high—about 1014 times that of water.
Many neutron stars are likely undetectable because they simply do not emit enough radiation.
Two general classes of non-quiet neutron star is pulsars star and magnetars star.