A galaxy that is an unusually powerful emitter of radio waves. The output of a radio galaxy can be up to 1038 watts, a million times greater than a normal galaxy such as our own. Radio galaxies have a compact radio nucleus coincident with the core of the visible parent galaxy, a pair of opposed jets emerging from the nucleus, and a pair of lobes (1) far outside the visible confines of the galaxy. The galaxy is almost always a giant elliptical, which may be the result of the collision and merger of two or more smaller galaxies. The source of the radio galaxy’s energy is believed to be a massive black hole in the galactic nucleus from which the jets emerge, delivering energy to the lobes. Notable radio galaxies include Centaurus A, Cygnus A, and Virgo A.
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A galaxy that is a strong source of electromagnetic waves of radio wavelengths. All galaxies, including our own, emit some radio waves, but radio galaxies are up to a million times more powerful.
In many cases the strongest radio emission comes not from the visible galaxy but from two clouds, invisible through an optical telescope, that can extend for millions of light years either side of the galaxy. This double structure at radio wavelengths is also shown by some quasars, suggesting a close relationship between the two types of object. In both cases, the source of energy is thought to be a massive black hole at the centre. Some radio galaxies are thought to result from two galaxies in collision or recently merged.
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