A pulsar is a small, dense star that emits a beam of electromagnetic radiation in a pulsing pattern as it rotates. Like a lighthouse light, the energy from a pulsar can be observed when it's pointing toward Earth.
Astronomers discovered pulsars in the 1960s, and they're still not sure exactly how they emit such huge amounts of radiation. They do know that pulsars spin, and that the "pulses" of energy have regular, precise spaces between them. Some pulsars emit radio waves, while others produce gamma ray or x-ray wavelengths. Pulsar comes from "pulse" or "pulsating star," and is modeled after quasar.