Neutron stars form from the stellar cores that remain after stars have exploded as Supernovae. (Supernova is a massive explosion in which the core of a massive star collapses in less than a second after it becomes a red super giant.) Sometimes the core survives the Supernova explosion. If the surviving core is about 1 1/2 to 3 times the mass of the sun, then it contracts to become a tiny dense NEUTRON STAR and if the surviving core is greater than 3 solar masses, then it becomes a BLACK HOLE. Neutron stars are normally 10 kilometres in diameter and consists almost entirely of neutrons (hence the name). Such stars are so dense that a spoonful would weigh about 1000000000000 Kg.
