Figure 24-1: Cygnus A (a) This false-color radio image from the Very Large Array shows that most of the emission from Cygnus A comes from luminous radio lobes located on either side of a peculiar galaxy. (Red indicates the strongest radio emission, while blue indicates the faintest). Each lobe extends about 230,000 ly) from the galaxy. (b) The galaxy at the heart of Cygnus A has a substantial redshift, so it must be extremely far from Earth (it is about 740 million ly). Only the very brightest central region of the galaxy is visible here. To be so distant and yet be one of the brightest radio sources in the sky, Cygnus A must have an enormous energy output.

(a: NRAO/AUI; b: Hubble Space Telescope, cropped from a mosaic of three images by Bill Keel)