Real Dictionary

pulsar
countable noun: A pulsar is a star that spins very fast and cannot be seen but produces regular radio signals.

pulsar in American English
any of several celestial objects, thought to be rotating neutron stars, which emit electromagnetic radiation, esp. radio waves, at short and very regular intervals
noun: one of several hundred known celestial objects, generally believed to be rapidly rotating neutron stars, that emit pulses of radiation, esp. radio waves, with a high degree of regularity

pulsar in British English
noun: any of a number of very small extremely dense objects first observed in 1967, which rotate very rapidly and emit very regular pulses of polarized radiation, esp radio waves. They are thought to be neutron stars formed following supernova explosions