What type of black hole is thought to power most active galactic nuclei?

A supermassive black hole is thought to power most active galactic nuclei.

These black holes contain hundreds of thousands to billions of Suns and reside at the centers of galaxies. When large quantities of gas fall toward one, friction and magnetic effects heat the accretion flow, producing enormous luminosity. The bright central source is called an active galactic nucleus, or AGN.

The black hole itself does not shine. Most of an AGN’s visible, ultraviolet, and X-ray output comes from hot material outside the event horizon, while jets can extend far beyond the host galaxy. A galaxy can contain a central supermassive black hole without being active if little gas is currently falling inward.

The Milky Way’s central black hole is relatively quiet today, whereas galaxies hosting quasars represent especially luminous AGN. Astronomers still investigate how such enormous black holes grew so early in cosmic history.