M1 - the Crab Nebula is a supernova remnant that lies about 6,500 light years away in the constellation of Taurus. The nebula was formed in 1054 when an exploding star was observed & recorded by Chinese astronomers.
The nebula is still expanding at a rate of 1,500 km per second, and the expansion can be seen by comparing photographs taken decades apart.
At the centre of the nebula lies a neutron star which is only approx 28-30 km diameter. It is spinning at 30.2 times per second, emitting pulses of radiation that range from radio through to gamma rays.
For more info. see the Wikipedia entry.