Astrophysics (index)

Active Galactic Nucleus

(central region of a galaxy with extremely high luminosity)

An Active Galactic Nucleus (AGN) is a central region of a Galaxy with very high Luminosity (L). Excess Emission has been observed in Radio, Infrared (IR), Visible Light, X-ray, and Gamma Rays wave bands. A galaxy hosting one is called an Active Galaxy.

The radiation is assumed to be due to Accretion of mass by a Supermassive Black Hole (SMBH). Often associated with a nucleus is a relativistic Jet. The radiation as well as matter spun from an Accretion Disk is called the AGN Outflow or AGN Feedback (see Star Formation Feedback) for which several possible effects are theorized:

  • Limitation to the rate that the Black Hole (BH) accrete matter.
  • Surrounding Cold Gas heated so it expands, slowing Star Formation (SF).
  • Surrounding cold gas compressed, increasing star formation, possibly leading to a starburst.

The outflow creates a region of Plasma whose heat causes it to have a lower density than the surrounding gas of the same pressure. The term AGN Bubble is used for the region. The plasma can give off X-Rays.

The extremely high luminosity of some AGNs (in theory, higher than could be sustained) has led to theories of pulses.

Some observed periodicity seems unlikely to be produced by a black hole, suggesting involvement of a Pulsar (PSR).


Referenced by:
Active Galaxy
Arakelian Catalog (Ark)
Cosmic X-Ray Background (CXB)
Gas Streamer
Helium Flash
Hyperluminous Infrared Galaxy (HLIRG)
Luminous Infrared Galaxy (LIRG)
Whirlpool Galaxy (M51a)
Quasar (QSO)
Quenched Galaxy
Rosat Bright Survey (RBS)
Relativistic Beaming
Seyfert Galaxy
Supermassive Black Hole (SMBH)
Submillimeter Galaxy (SMG)
Tidal Disruption Event (TDE)
Ultraluminous Infrared Galaxy (ULIRG)
Ultraluminous X-Ray Source (ULX)
Wide-Field Infrared Survey Explorer (WISE)