active galaxy


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active galaxy

A galaxy that is emitting unusually large amounts of energy from a very compact central source – hence the alternative name active galactic nucleus or AGN. (A separate category, starburst galaxy, is employed for a galaxy where a high infrared luminosity arises from intense star formation.) The central powerhouse may be observed directly, as in Seyfert galaxies, BL Lac objects, or quasars; in radio galaxies it is the radio-emitting lobes created by beams emanating from the powerhouse that are observed. In general the host galaxies of powerful AGN are large, luminous elliptical galaxies, whereas the hosts of Seyferts are spiral. Although some radio-quiet QSO are found located in disklike hosts, most are found to lie in elliptical galaxies.

Observations of the motions of stars and gas in galaxies such as M87 (see Virgo A) and NGC 4151 (see Seyfert galaxy), in addition to other arguments (see quasar; power-law spectrum), strongly suggest that the energy output is derived from the gravitational potential of a supermassive black hole: the energy arises from an accretion disk of matter spiraling into the black hole. This material could come from the interstellar medium of a spiral galaxy (especially when perturbed by gravitational effects in interacting galaxies), from the tidal disruption of stars near the black hole, or from flows of intergalactic gas on to the central galaxy of a cluster of galaxies, as the gas cools. The X-ray continuum spectrum of many AGN features components of emission that are thought to be reflected off the accretion disk of the black hole, producing a reflection spectrum.

active galaxy

[′ak·tiv ′gal·ək·sē]
(astronomy)
A galaxy whose central region exhibits strong emission activity, from radio to x-ray frequencies, probably as a result of gravitational collapse; this category includes M82 galaxies, Seyfert galaxies, N galaxies, and possibly quasars.
References in periodicals archive ?
The active galaxy that has now been identified is a so-called blazar, an active galaxy whose jet points precisely in our direction.
"We either have a system of two supermassive black holes with the disk-ejecting jet forced to wobble by tidal effects of the secondary black hole or a single black hole that is tidaly interacting with a misaligned accretion disk," concludes Christian Fendt from the Max Planck Institute for Astronomy (MPIA) in Heidelberg.Either way, the jet of the active galaxy OJ 287 is one of the best understood jets so far and will certainly be used to decipher other extragalactic jets as well.
Additionally, many more distant galaxies are visible; sitting at the outskirts of the spiral arms, they appear tiny and delicate compared to the colossal active galaxy .
Nearby, about 2[degrees] east of brilliant Algol, lies a real monster, an active galaxy that dominates the Perseus Galaxy Cluster.
Samsung previously reported about 85 percent of the active Galaxy Note 7 handsets had been recovered through its recall process, leaving several hundred thousand still active and at risk of explosion.
He explores such topics as redder than red, making electrons from photons, the outer solar system and the problem of Pluto, stellar death, the origin of the initial mass function, the active galaxy menagerie, the most distant galaxies known, a brief history of the universe, and the Space Infrared Telescope for Cosmology and Astrophysics (SPICA).
Washington, March 14 ( ANI ): Researchers have obtained the most detailed view so far of the warm dust in the environment of a supermassive black hole in an active galaxy.
Astronomers classify B0218+357 as a blazar -- a type of active galaxy noted for its intense emissions and unpredictable behavior.
Astrophysicist Marco Ajello of Stanford and his colleagues used the orbiting Fermi Large Area Telescope to study distant blazars, a type of bright, active galaxy. Blazars are powered by supermassive black holes that shoot enormous jets toward Earth.
Samsung reported (http://www.androidauthority.com/samsung-85-percent-galaxy-note-7-phones-replaced-726910/) 85 percent of the active Galaxy Note 7 handsets had been recovered.
However, the active galaxy in this new study, Markarian 1018 stands out by having changed type a second time, reverting back to its initial classification within the last five years.
In January of last year, supernova 2014J erupted in the nearby active galaxy M82 in Ursa Major.