4.1.4. Formation of Supernova Star and Neutron Star

When a very big star is in the red-giant phase, then being big, its core contains much more helium. This big core made up of helium continues to contract (shrink) under the action of gravity producing higher and higher temperature. At this extremely high temperature, fusion of helium into carbon takes place in the core and lot of energy is produced. Since the star was very big and contained enormous nuclear fuel helium, so a tremendous amount of nuclear energy is produced very rapidly which causes the outer shell (or envelope) of this red-giant star to explode with a brilliant flash like a nuclear bomb. This type of ‘exploding star is called supernova. The energy released in one second of a supernova explosion is equal to the energy released by the sun in about 100 years. This tremendous energy would light up the sky for many days. When a supernova explosion takes place, then clouds of gases in the envelope of red-giant star are liberated into the space and these gases act as raw material for the formation of new stars. The heavy core left behind after the supernova explosion continues to contract and ultimately becomes a neutron star (if mass of star was 1.44 time to 3 times the Sun) or Black Hole (if the mass of star was more than 3 times the sun).

A neutron star contains matter in even denser form than found in white dwarf stars. Although a number of white dwarfs have been detected, but no one has yet observed a neutron star. This may be because neutron stars are very faint. A spinning neutron star emits radio waves and is called a pulsar.