What evidence do we have that pulsars are neutron stars?

Why are some stars known as pulsars?

The heaviest stars die explosively, signalling their end with a brilliant flash of light called a supernova. Astronomers know that a supernova’s radiance is not quite the finish, but it is without doubt the beginning of the end.

When a supernova dies, it leaves behind a small ball of highly concentrated matter, composed entirely of subatomic particles known as neutrons. This discovery was made by two British radio astronomers, Anthony Hewish and Jocelyn Bell. In 1967, they picked up strange but regular signals from outer space. Dismissing the idea that the signals came from inhabitants of some other civilisation, they realised they had found a source of pulsating energy in space.

Since that discovery at Cambridge, England, astronomers have found hundreds of other radio beacons in the skies, and say that a million more exist, waiting to be identified. These stars flash signals in much the same way that the rotating lantern of a lighthouse sends out a distinctive message. They are the remnants of supernovas, are only some 25 km (15k miles) in diameter, and vary in their rate of spin. The fastest rotates at about 642 revolutions per second; others turn only once in that time.

Like lighthouses, spinning beacons are readily identified, because their radiation sweeps across the skies, giving out a steady pulselike beat. For this reason, these stars are known as pulsars.

Pulsars, or neutron stars, consist of matter compressed so tightly that it is difficult for us to comprehend. If we could recover a pinhead sized piece of a neutron star, it would weigh about a million tonnes roughly equal to twelve vessels the size of the USS Nimitz, the world’s largest warship.

The gravity on a neutron star is so intense that, if by some misfortune you were to land on one, you would suffer instant death. The force would flatten your body, spreading it thinner and thinner over a wide area until it could be flattened no more. Finally, you would become a wafer of crushed flesh and bone just one atom thick.