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Cab nebula (M1). Optical image of the Crab nebula, the remnant of a supernova. In the centre of the nebula is the remains of the star's core, which has formed a pulsar (white dot), or neutron star rotating 30 times a second and emitting regular pulses of radiation. 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. The crab nebula lies 6000 light years from Earth in the constellation Taurus. Imaged by the 0.9M telescope of the West Mountain Observatory, Utah, USA. (KEYSTONE/SCIENCE PHOTO LIBRARY/ROBERT GENDLER/SCIENCE PHOTO LIBRARY)