Pulsar from a planet. Artwork of a pulsar from the surface of a planet orbiting it. Whirls of fluorescing gas are seen in the sky, trapped by the intense magnetic field of the pulsar. A pulsar is a rapidly spinning neutron star, the remnant of a massive star that exploded as a supernova. It has the mass of the Sun condensed into a globe around 10 kilometres in diameter. Two beams of radiation, usually radio waves, are emitted from the pulsar. From Earth these are detected as flashes of radiation, separated by between a few milliseconds and a few seconds. Unless the pulsar's beam hits Earth, it will not be identified as a pulsar.