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. Such atypical emission has been observed in radio, infrared, visible light, X-ray, and gamma-ray bands. A galaxy hosting an AGN 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 other X-ray sources strong enough to create any doubt. The radiation is assumed to be due to accretion of mass by a supermassive black hole at the center of the galaxy. Often associated with an AGN 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 temperature 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. AGNs are sometimes classified using a classification that originated with Seyfert galaxies, which harbor AGNs. Some classes of AGN:

(galaxies,quasars,EMR,galaxy nucleus)
Further reading:

Referenced by pages:
accretion rate
active galaxy
AGN corona
Arakelian Catalog (Ark)
Balmer jump (BJ)
broad emission line region
black hole accretion rate (BHAR)
bipolar outflow
broad-line region (BLR)
Chandra Deep Field South (CDFS)
Compton reflection
cosmic X-ray background (CXB)
Cygnus A (3C 405)
direct collapse black hole (DCBH)
extragalactic astronomy
star formation feedback
Fanaroff-Riley classification
galactic astronomy
galactic wind
galaxy merger
gas streamer
gravitational collapse
gravitational lensing
high-energy astrophysics (HEA)
hyperluminous infrared galaxy (HLIRG)
hot DOG
ionizing radiation
iron (Fe)
jet current
luminous infrared galaxy (LIRG)
LaSilla-QUEST Variability Survey (LSQ)
Whirlpool Galaxy (M51a)
Meier paradox
gravitational microlensing
N galaxy
obscured fraction-luminosity relation
plasma astrophysics
Poynting vector (S)
quasar (QSO)
quenched galaxy
radiation pressure
Rosat Bright Survey (RBS)
relativistic beaming
retrograde accretion
radio galaxy (RG)
radio source (RS)
Seyfert galaxy (Sy)
supermassive black hole (SMBH)
superluminal motion
tidal disruption event (TDE)
thermal dust emission
Thomson optical depth (τT)
3C 273
transient astronomy
ultra-fast outflow (UFO)
ultraluminous infrared galaxy (ULIRG)
ultraluminous X-ray source (ULX)
ultraviolet astronomy
Wide-field Infrared Survey Explorer (WISE)
X-ray luminosity function (XLF)
X-ray source