active galactic nucleus

(redirected from Active galaxies)
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Related to Active galaxies: Quasars

active galactic nucleus

(AGN) See active galaxy.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006

active galactic nucleus

[¦ak·tiv gə‚lak·tik ′nü·klē·əs]
(astronomy)
A central region of a galaxy, a light-year or less in diameter, where violent and apparently explosive behavior is observed which is manifested in many ways, including the high-velocity outflow of gas, strong nonthermal radio emission, intense and often polarized and highly variable radiation over a wide range of wavelength bands, and ejection of jets of relativistic material.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The astronomers initially selected this galaxy to validate accepted models about lower-luminosity active galaxies -- those with black holes that are on a meager diet of material.
The time in Texas indeed shaped much of Tony's later research career; his interest in active galaxies and supernovae (valuable for measuring the scale of the universe) were strengthened from the time spent in California with Fritz Zwicky, whom Tony held in the highest regard.
Aimed at astronomy and physics majors, it offers thorough coverage of galactic structure and evolution, active galaxies, cosmology, and the history of the universe.
Activities include: (1) Building Perspectives with Active Galaxies; (2) Zooming In on Active Galaxies; and (3) Light Travel Time and the Size of Active Galaxies.
During the first five years - its original lifespan was only meant to be three to five years - cosmonauts and scientists pushed back the limits of knowledge on the physics of active galaxies, quasars and neutron stars, and acquired a wealth of information about living for long periods in space.
Active galaxies are a special class of galaxies: 1-2% of the whole population of galaxies, which shine with more energy than their stars alone can provide.
This was the first case of what came to be called active galaxies, those with centers that seem to be the site of activity beyond the normal.
While such winds are now found in many active galaxies, PG1211+143 has now yielded another 'first', with the detection of matter plunging directly into the hole itself."
Same is the job of their elder siblings that are much bigger in size and are found at the heart of active galaxies.
Special types of distant active galaxies and their innermost central regions show extreme physical processes.
Using data from NASA's Rossi X-ray Timing Explorer (RXTE) satellite, an international team has uncovered a dozen instances where X-ray signals from active galaxies dimmed as a result of a cloud of gas moving across our line of sight.