Definitions for "Active galactic nucleus"
A galaxy is said to have an active nucleus if unusually violent events are taking place in its center, emit-ting large quantities of electromagnetic radiation. Seyfert galaxies and quasars are examples of galaxies with active nuclei.
The central portion of a galaxy which gives off unusually large amounts of energy. These are thought to be powered by supermassive Black Holes.
A very bright, compact region found at the center of certain galaxies. The brightness of an active galactic nucleus is thought to come from an accretion disk around a supermassive black hole. The black hole devours matter from the accretion disk, and this infall of matter provides the firepower for quasars, the most luminous type of active galactic nucleus.