Crab Nebula (M1) in Taurus. This is a supernova remnant, a shell of gas expanding from the explosive death of a massive star. The supernova that created this remnant was recorded by early astronomers in 1054, and was visible in daylight for 23 days. A supernova is the death of a massive star. Once it runs out of fuel for nuclear fusion the layers collapse into a central neutron star. The outer layers fall on this, ignite and rebound with an enormous amount of energy. A neutron star may have the mass of the Sun in a region just 10 kilometers across. This supernova remnant lies around 6500 light years from Earth in the constellation Taurus.