Crab Nebula (M1; NGC 1952)

The nebulous remnant in the constellation Taurus of a supernova that exploded in AD 1054. In coloured photographs it appears as a network of red filaments surrounding an elliptical area of pale white light. This white light is synchrotron radiation generated by hot ionized gas in a magnetic field. The filaments are the outer layers of the star that were blown off in the explosion and are travelling outwards at about 1,500 km/s. The core of the star that exploded remains at the centre of the nebula. It is now a pulsar. Electrons emitted by the pulsar are responsible for the synchrotron radiation. The interval between flashes from the pulsar is 33 milliseconds; flashes are seen in visible light as well as the radio pulses. The Crab Nebula is one of the strongest sources of radio waves in the sky; this source was called "Taurus A" by radio astronomers before it was identified with the known nebula. It is also a source of X-rays.