"At the [Crab Nebula's] core lies a pulsar, a type of neutron star, discovered by radio astronomers in 1968. Only 12 miles [19 kilometers] across, it spins 30 times a second, spewing out high-energy particles. As particles flow out, they lose energy and emit radiation in longer wavelengths. Highlighted in false color, an optical image shows intermediate-energy particles from the pulsar (blue) along with material ejected into space by the supernova explosion itself (green and red)."
From "Super X-ray Vision," December 2002, National Geographic magazine