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Cygnus AAn intense radio source in Cygnus that has a flux density at 178 megahertz of 8100 jansky. It is a typical double radio source (see illustration at radio-source structure) and is identified with a 16-magnitude radio galaxy; a narrow radio jet connects the central galaxy to the NW lobe. The galaxy has a redshift of 0.057, indicating a distance of about 230 megaparsecs, and a spectral index of –0.8 below 1 GHz. It is the brightest low-redshift radio source, with a radio luminosity more typical of very distant radio galaxies (those above a redshift of one).
The galaxy is at the center of a cooling flow cluster (see clusters of galaxies), and its optical spectrum is rich in forbidden emission lines. It also contains a polarized blue continuum that is due to scattered light from a hidden quasar nucleus.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
Cygnus A[′sig·nəs ′ā]
A strong, discrete radio source in the constellation Cygnus, associated with two spiral galaxies in collision.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.