Crab Nebula. Hubble Space Telescope image of the interior of the Crab Nebula supernova remnant (M1). Different elements are colour-coded: sulphur (pink), nitrogen (red), hydrogen (orange) and oxygen (green). These gases were expelled as a 10 solar mass star exploded as a supernova, an event witnessed by Chinese astronomers in 1054 AD. The core of the star survived as a pulsar, a rapidly- spinning neutron star (lower of the two bright stars just above and left of centre). The rotation of this star heats the surrounding gas, causing the blue glow seen here. Image from the Wide Field and Planetary Camera 2 on the HST.