A mysterious, "quasistellar", or star-like, object in a galaxy's core which is very small, very bright, and very distant: Most quasars are strong sources of radio energy.

A quasar is an exceptionally powerful, yet very compact extragalactic object, whose exact nature is still uncertain.

Observations suggest that quasars may be the hyperactive nuclei of galaxies, while theory indicates that the high luminosity which is 100 to 1,000 times that of normal galaxies, could be associated with a supermassive black hole.