Crab Pulsar

The pulsar at the centre of the Crab Nebula. In 1942, astronomers had speculated that a peculiar star in this nebula was a neutron star, created in the supernova of AD 1054. Radio astronomers discovered in 1968 that the central star is a pulsar spinning 30 times a second; the period between pulses is thus 33 milliseconds. Shortly after discovery of the radio pulsar, the visible light from the neutron star was also shown to be pulsed. At the time of discovery, this was the fastest pulsar by far and the spin rate indicated unambiguously that the object must be a neutron star: any object with a typical star's mass but larger than a neutron star would fly apart at the rotation rate seen in the Crab Pulsar. Historically, the discovery is of great importance because theorists subsequently felt much more confident that highly condensed objects really do exist in the universe. This led directly to research on black holes. The Crab pulsar is a source of electrons travelling at almost the speed of light that give rise to strong X-ray and radio emission from the Crab Nebula itself. The pulsar's rotation period is increasing at 36 nanoseconds per day, at which rate its rotation speed will be halved within about 1,200 years. The pulsar has random glitches, which may be caused by starquakes. The mass is thought to be about half that of the Sun.