The region at the center of certain galaxies from which an enormous amount of energy is released. It is believed that this energy comes from matter accreting via an accretion disk on to a supermassive black hole of more than 100 million solar masses. All the various forms of AGN may come from a single type of source whose appearance depends on its orientation relative to the observer. The AGN may consist of a compact source surrounded by a torus doughnut-shaped ring of gas and dust. Narrow jets of gas are emitted at velocities approaching the speed of light along the axis of rotation, which is at right angles to the ring. If the line of sight were through the torus, the central source would be obscured, and the AGN would appear to be a radio galaxy. If the torus were tilted toward the line of sight, the central source would be visible, and the AGN would be seen as a quasar. Looking directly along, or close to, the jet, would result in the appearance of a blazar.