pulsar - (n.)
A rapidly rotating object, now known to be a neutron star, an extremely dense collapsed star where the electrons have been forced into the protons. The object is thus made up mainly of neutrons and a few kilometers in diameter. Pulsars emit magnetic field constrained beams of radio, visible, x-ray and gamma radiation, which we perceive as pulses as these objects whirl, sometimes at hundreds of revolutions a second.