Crab Nebula

The Crab Nebula is a supernova remnant and pulsar wind nebula in the constellation of Taurus. Corresponding to a bright supernova recorded by Chinese astronomers in 1054, the nebula was observed later by John Bevis in 1731.

The Crab Nebula was first identified in 1731 by John Bevis. The nebula was independently rediscovered in 1758 by Charles Messier as he was observing a bright comet

It was named by Lord Rosse for its superficial resemblance to a crab. The Crab is 6 by 4 in extent and of eighth magnitude. Its outer regions consist of twisting filaments of hydrogen expelled by the supernova, appearing red on photographs and traveling outward at over 1000 km s−1. The inner region glows with the pale yellow light of synchrotron radiation triggered by electrons emitted by the Crab Pulsar at the center, the
core of the star that exploded as a supernova. This inner region makes the Crab Nebula the best-known example of a plerion—a supernova remnant with a ‘filled’ center. The Crab emits strongly in radio waves and x-rays.

• Distance to Earth: 6,523 light years
• Age: 1,000 years

At the center of the nebula lies the Crab Pulsar, a neutron star 28–30 km across, which emits pulses of radiation from gamma rays to radio waves with a spin rate of 30.2 times per second. The nebula was the first astronomical object identified with a historical supernova explosion.

At the centre of the Crab Nebula are two faint stars, one of which is the star responsible for the existence of the nebula. It was identified as such in 1942, when Rudolf Minkowski found that its optical spectrum was extremely unusual.The region around the star was found to be a strong source of radio waves in 1949and X-rays in 1963, and was identified as one of the brightest objects in the sky in gamma rays in 1967.Then, in 1968, the star was found to be emitting its radiation in rapid pulses, becoming one of the first pulsars to be discovered.

Pulsars are sources of powerful electromagnetic radiation, emitted in short and extremely regular pulses many times a second. They were a great mystery when discovered in 1967, and the team who identified the first one considered the possibility that it could be a signal from an advanced civilization.However, the discovery of a pulsating radio source in the centre of the Crab Nebula was strong evidence that pulsars were formed by supernova explosions. They now are understood to be rapidly rotating neutron stars, whose powerful magnetic field concentrates their radiation emissions into narrow beams.