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 total entropy of the universe and of a single active galaxy sums to zero.
Before changing direction, continue another 8' southwest to find active galaxy IC 310, which seems almost easy after so many eye-straining targets.
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.
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.
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.
Summary: TEHRAN (FNA)- ESO's Very Large Telescope Interferometer gathered the most detailed observations ever of the dust around the huge black hole at the center of an active galaxy.
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.
com/samsung-85-percent-galaxy-note-7-phones-replaced-726910/) 85 percent of the active Galaxy Note 7 handsets had been recovered.
In January of last year, supernova 2014J erupted in the nearby active galaxy M82 in Ursa Major.
CU-Boulder Professor Michael Shull and Research Associate David Syphers used the Hubble Space Telescope to look at the quasar-the brilliant core of an active galaxy that acted as a "lighthouse" for the observations-to better understand the conditions of the early universe.
Lamer and his Potsdam colleagues first spotted the massive cluster, dubbed 2XMM J083026+524133, when scrutinizing data from the European Space Agency's XMM-Newton telescope, which captured the cluster's signature in 2001 while imaging a distant, active galaxy.
Scientists believe that sometime in the not-so-distant past, Markarian 1018 began merging with another active galaxy.