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A member of a class of giant elliptical galaxies with an extended halo of stars. The designation was introduced by W. Morgan in the late 1950s. A cD galaxy is often found to be the central galaxy in a rich cluster, and many are also radio emitters. They are five to ten times more luminous than typical elliptical galaxies and their mass may be as high as 1013 solar masses. A classic example is NGC 6616, which appears to have multiple nuclei within its envelope and is thought to be "swallowing" smaller galaxies in its vicinity.
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