What formed the Crab Nebula?
The Crab Nebula is a supernova remnant created by the explosion of a massive star.
In 1054 AD there are records of a new star appearing in the sky in the constellation Taurus. This guest star was so bright that it was visible even during the day. Later, Charles Messier observed the Crab Nebula and included it as the first entry in his catalog.
Eventually astronomers were able to measure the speed at which the nebula was expanding. They calculated that the explosion date and found that it coincided with the date of the guest star, establishing that the two events were related.
The Crab Nebula also has a pulsar, a neutron star which spins incredibly fast. Since neutron stars are created during a supernova, the pulsar is further proof that the nebula is a supernova remnant.