Crab nebula (M1). This is the remnant of a supernova. The supernova was recorded 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. It lies 6000 light years from Earth in the constellation Taurus. Different colours represent different ionised gases; sulphur is red, hydrogen is green and oxygen is blue.