An AGN is thought to turn on when a lot of gas falls onto a black hole in the centre of a galaxy. The gas forms an accretion disk and heats up and radiates according to thermal bremsstrahlung radiation.
AGN fall into two major divisions: radio-loud and radio-quiet. Within each is a broad range of luminosity, ...
An AGN is short for "Active Galactic Nucleus." Some galaxies have nuclei (centers) that are 'active', meaning they emit large amounts of radiation (radio, optical, X-rays, gamma-rays, particle jets, etc.), and/or are highly variable.
In real AGN spherical accretion is not reasonable; gas in galaxies will have some net angular momentum, and the transverse veliocity is amplified during infall.
Definition: active galactic nuclei (AGN): A class of galaxies which spew massive amounts of energy from their centers, far more than ordinary galaxies.
AGN -- An unusually bright galactic nucleus whose light is not due to starlight.
Active Galaxy ...
AGN are thought to be powered by centrally located, supermassive black holes. The central regions of all AGN are thought to be similar and are explained by the Unified Model of AGN.
AGN are likely switched on by galaxy collision and mergers. "If two galaxies collide and each possesses a supermassive black hole, there should be times when both black holes switch on as AGN," says Mushotzky.
AGN terminology is often confusing, since the distinctions between different types of AGN sometimes reflects historical differences in how objects were discovered or initially classified, rather than real physical differences.
Radio-quiet AGN ...
Blazars are AGN with a relativistic jet that is pointing in the general direction of the Earth. We observe "down" the jet, or nearly so, and this accounts for the rapid variability and compact features of both types of blazars.
Objects with a great variety of names - QSOs (or quasars), blazars, Seyfert galaxies, radio galaxies, and sometimes liners(low ionization nuclear emission line galaxies) - are all grouped into the category active galactic nuclei (AGN) because they ...
From it pours a variable jet at nearly the speed of light, making M 87 an "active galaxy" and the core an "active galactic nucleus," or "AGN.
Active galactic nuclei (AGN) are galaxies that have a massive black hole at the galactic center (nucleus). These galaxies produce huge amounts of energy (at all wavelengths of the electromagnetic spectrum).
Active Galactic Nucleus (AGN)
A very bright, compact region found at the center of certain galaxies. The brightness of an active galactic nucleus is thought to come from an accretion disk around a supermassive black hole.
Active Galactic Nucleus (AGN): The central region of an active galaxy where the energtic activity is concentrated.
active galactic nuclei (AGN)
It is believed that these are normal galaxies with a massive black hole accreting gas at its center, thus producing enormous amounts of energy at all wavelengths of the electromagnetic spectrum.
Active Galactic Nuclei (AGN): A galaxy with an unusually bright central region thought to contain a supermassive black hole actively pulling in tremendous amounts of matter from a swirling disk of gas, stars, and dust.
active galactic nucleus (AGN): The central energy source of an active galaxy.
active galaxy: A galaxy that is a source of excess radiation, usually radio waves, X rays, gamma rays, or some combination.
Firstly X-rays are emitted by black holes in active galactic nucleus, or AGN for short, galaxy clusters, supernova remnants, stars, binary stars containing a white dwarf (cataclysmic variable stars), neutron star or a black hole (X-ray binaries), ...
active galactic nuclei (AGN)
The centers of active galaxies that are emitting large amounts of excess energy.
active galaxy ...
So, it is also termed the active galactic nuclei (AGN). We are not completely sure how an active galaxy is formed and how it generates such a large amount of energy. One of the most popular hypothesis is the supermassive black hole theory.
One question remains unanswered by astronomers: Because we see quasars exclusively at great distances -- and, therefore, the light we detect from them comes from a long time ago -- does this mean that all galaxies have had an AGN in their center at ...
Distant galaxies - Hubble images
Quasars - Hubble Images
NASA AGN site
Bill Keel's AGN site ...
active galaxy, active galactic nucleus, AGN
radio wavelengths, radiowaves
bremsstrahlung radiation ...
The central region of an active galaxy is called an "active galactic nucleus" (AGN) where energetic activity is concentrated.
are many cluster located there, the main reason for Lacerta's fame is BL Lacertae. This object, originally identified as an irregular variable star, is now known to correspond to a quasi-stellar object a.k.a. an active galactic nucleus (AGN).
such as the Chandra X-ray Observatory, have demonstrated that around 80% of the cosmic X-ray background is due to resolved extra-galactic X-ray sources, the bulk of which are unobscured ("type-1") and obscured ("type-2") active galactic nuclei (AGN).
 See also: Galaxies, Galaxy, Energy, Light, Universe
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