fossil group
n.— «All that dark matter makes astronomers think that NGC 1132 grew up through the mergers of many smaller galaxies in an entire group, drawn in by the dark matter. That’s why the galaxy is sometimes called a “fossil group.” However, they can’t rule out a scenario in which NGC 1132 was born as a full-fledged giant—perhaps under conditions that somehow suppressed the formation of lesser galaxies.» —“See A Dark-matter Magnet” by Alan Boyle MSNBC: Cosmic Log Feb. 5, 2008. (source: Double-Tongued Dictionary)
Further reading
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