Astronomy. A discrete source of radio waves outside the solar system (often subsequently identified as a galaxy). Now chiefly historical.

any compact celestial emitter of X-rays (not necessarily a star), such as an X-ray binary or an X-ray pulsar.

quasi-stellar source (of radio waves).

a celestial object that is a very strong but transient emitter of X-rays, typically a binary system with either a neutron star or a black hole as the…

Astronomy. A weaker pulse occurring between the main pulses of radiation from some pulsars.

a receptor in an X-ray binary that is a pulsar.

a celestial emitter of X-rays that has two components, with matter passing from one component (the donor) to the other (the accretor) giving rise…