Active galaxy, illustration. Active galaxies are those with an active galactic nucleus (AGN), driven by a central supermassive black hole. AGNs emit a range of non-stellar radiation, including radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray radiation. The features commonly seen in an AGN are the opaque torus, an accretion disc around the central supermassive black hole, and relativistic jets, which are beams of ionised matter accelerated close to the speed of light.