The outer layers being ejected create an expanding shell of dust and gas that become a supernova remnant. The Birth of Neutron Stars Besides the interstellar debris, supernova explosions often leave behind a cinder, the star's dense, collapsed neutron core, which was created by the compression of electrons and protons. Called a neutron star, the object is about 10 miles wide, has a mass greater than our Sun, and a density of about a billion tons per teaspoonful. 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.