What is a rapidly spinning neutron star that emits radio waves called?

A rapidly spinning neutron star that emits beams of radio waves is known as a pulsar. This phenomenon occurs when the neutron star rotates and the magnetic axis is tilted relative to the rotation axis. As the star spins, it emits beams of electromagnetic radiation from its magnetic poles. If these beams are oriented such that they sweep across the Earth, they can be detected as pulses of radiation, hence the name "pulsar."

Pulsars are fascinating astrophysical objects that provide insights into the nature of neutron stars and the conditions in extreme gravitational environments. Their precise rotation periods can be measured, which allows scientists to use them as cosmic clocks in various astrophysical research contexts.