Tidal tail

A galactic tide is a tidal force subjected on objects by the gravitational field of a galaxy such as the Milky Way. Particular areas of interest concerning galactic tides include galactic collisions, the disruption of dwarf or satellite galaxies, and the Milky Way's tidal effect on the hypothesized Oort Cloud of our own solar system.
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A tail-like structure of stars which has been flung out behind galaxies when they undergo a galaxy merger. The tails are produced by the galaxies falling into each other's potential wells.