Because of its small size and high density, the neutron star possesses a gravitational field 300,000 times stronger than the Earth's. Its rotation also increases dramatically during the collapse. Most celestial objects rotate, but neutron stars rotate very rapidly. The neutron star in the Crab Nebula rotates 30 times per second or 3.4 million miles per hour. It is the only kind of star that can rotate rapidly without breaking apart.
Astronomers pick up the radio waves only when the pulsar's beam sweeps across the Earth.
Pulsars possess a powerful magnetic field that traps and accelerates charged particles, and shoots them through space as radio waves. Their rapid rotation makes them powerful electric generators, capable of accelerating charged particles to energies of millions of volts. The Crab, the youngest and most energetic pulsar, produces enough energy to power the nebula and make it expand. A pulsar's energy output lights up and expands the nebula around it. This action robs energy from the pulsar's rotation, so that it spins slower over time.