active galactic nucleus
(AGN)
(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 (SMBH) 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:
- Limitation to the rate that the black hole accrete matter.
- Surrounding cold gas heated so it expands, slowing star formation.
- Surrounding cold gas compressed, increasing star formation, possibly leading to a starburst. Note that subsequent to such a burst, cold gas may be depleted and star formation minimal.
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:
- NLAGN (narrow-line AGN, Type 2 AGN) versus BLAGN (broad-line AGN, Type 1 AGN): based upon the width of emission lines which is taken as Doppler broadening, indicating radial velocity of the source of the spectral line, i.e., motion of the gas/plasma.
- LLAGN (low-luminosity AGN): a lower X-ray emission than a typical AGN, though it is possible the LLAGNs are the more frequent.
Some AGNs (termed changing-look AGNs) change from one such type or
classification to anther as time passes.
(galaxies,quasars,EMR,galaxy nucleus)
Further reading:
https://en.wikipedia.org/wiki/Active_galactic_nucleus
https://astronomy.swin.edu.au/cosmos/a/Active+Galactic+Nuclei
https://hea-www.harvard.edu/~wmaksym/agnfeedback.html
http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/actgal.html#c2
https://ui.adsabs.harvard.edu/abs/2017FrASS...4...42M/abstract
https://webbtelescope.org/contents/articles/what-are-active-galactic-nuclei
Referenced by pages:
3C 273
accretion rate
ACIS
active galaxy
AGN accretion
AGN corona
Arakelian Catalog (Ark)
Baldwin effect
Balmer jump (BJ)
BASS
Bethe-Heitler process
bipolar outflow
black hole accretion rate (BHAR)
blazar
BPT diagram
broad line region (BLR)
Catalog of Galaxies and Clusters of Galaxies (CGCG)
Centaurus A
Chandra Deep Field South (CDFS)
Cloudy
Compton reflection
corona
Cosmic Evolution Survey (COSMOS)
cosmic gamma ray background (CGB)
cosmic X-ray background (CXB)
Cygnus A (3C 405)
direct collapse black hole (DCBH)
duty cycle
extragalactic astronomy
Fanaroff-Riley classification
galactic astronomy
galactic wind
galaxy merger
galaxy SED
gas streamer
gravitational lensing
gravitational microlensing
high-energy astrophysics (HEA)
hot DOG
HXMT
hyperluminous infrared galaxy (HLIRG)
infrared excess (IRX)
ionizing radiation
iron (Fe)
IXPE
jet
jet current
K-line
Kelvin-Helmholtz mechanism (KH mechanism)
LaSilla-QUEST Variability Survey (LSQ)
LINER
luminous infrared galaxy (LIRG)
Lyman break (LB)
Lyman-alpha blob
M87*
magnetically arrested disk (MAD)
maser
Meier paradox
microwave
MOJAVE
N galaxy
narrow line region (NLR)
NGC 1052
NGC 2363
NGC 7469
obscured fraction-luminosity relation
Penrose Compton scattering (PCS)
PESSTO
plasma astrophysics
Poynting vector (S)
quasar (QSO)
quenched galaxy
radiation pressure
radio galaxy (RG)
radio source (RS)
radio star
relativistic beaming
relic
retrograde accretion
reverberation mapping
Rosat Bright Survey (RBS)
Seyfert galaxy (Sy)
silicon monoxide (SiO)
spectral temperature
spectropolarimetry
star formation feedback
superluminal motion
supermassive black hole (SMBH)
thermal dust emission
Thomson optical depth (τT)
tidal disruption event (TDE)
time-delay cosmology
transient astronomy
ultra-fast outflow (UFO)
ultraluminous infrared galaxy (ULIRG)
ultraluminous X-ray source (ULX)
ultraviolet astronomy
Whirlpool Galaxy (M51a)
Wide-field Infrared Survey Explorer (WISE)
X-ray
X-ray luminosity function (XLF)
X-ray source
XBONG
Index