Crab nebula (M1), optical image. The Crab nebula is the remnants of a supernova, or death of a large star. The supernova was recorded as a bright, temporary 'star' by Chinese astronomers in 1054. When a large star dies, gas shells explode outwards and collide with interstellar material. The energy of the collision ionises the gas, causing it to glow. In the centre of the nebula is the remains of the star's core, which has formed a pulsar, or neutron star rotating 30 times a second and emitting regular pulses of radiation. The Crab nebula lies 6300 light years from Earth in the constellation Taurus.