When a star heavier than the Sun runs out of hydrogen, it blows away its outermost gases and collapses into its core. This dense rotating object is called a neutron star. These rotating celestial objects give out x rays and radio waves like gamma rays when they turn towards the earth. As they rotate, it appears like a flash of light appearing (when they point towards the earth) and disappearing (when they point away from earth), giving the impression that the neutron star is pulsating. Hence they are known as pulsars. These neutron stars are composed of subatomic particles called neutrons. These have a very strong magnetic field and electrical field.
The time period between the beginning of one pulse to the beginning of the next is called pulse period. It ranges from about one thousandth of a second to more than four seconds. Pulsars with a period close to a thousandth of a second are known as millisecond pulsars. Though they are heavier than the sun, the diameter is less than 20 miles of that of sun’s diameter. Thus, it emits radiations from a small area that faces the earth for a brief amount of time.
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