Astrophysics (index)about

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. Excess emission has been observed in radio, infrared, visible light, X-ray, and gamma rays bands. A galaxy hosting one is called an active galaxy. X-rays are useful for identifying AGNs because virtually all produce them and they penetrate the surrounding galaxy, which have no X-ray sources strong enough to lead to confusion.

The radiation is assumed to be due to accretion of mass by a supermassive black hole. 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:

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.

(galaxies,quasars,EMR,galaxy nucleus)

Referenced by:
accretion rate
active galaxy
Arakelian Catalog (Ark)
Chandra Deep Field South (CDFS)
cosmic X-ray background (CXB)
Fanaroff-Riley classification
galaxy merger
gas streamer
gravitational collapse
gravitational lensing
helium flash
hyperluminous infrared galaxy (HLIRG)
hot DOG
jet current
luminous infrared galaxy (LIRG)
Whirlpool Galaxy (M51a)
N galaxy
Poynting vector (S)
quasar (QSO)
quenched galaxy
Rosat Bright Survey (RBS)
relativistic beaming
Seyfert galaxy
supermassive black hole (SMBH)
submillimeter galaxy (SMG)
superluminal motion
tidal disruption event (TDE)
ultraluminous infrared galaxy (ULIRG)
ultraluminous X-ray source (ULX)
Wide-field Infrared Survey Explorer (WISE)