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galaxy interaction

interacting galaxies
Grazing encounter between the spiral galaxies NGC 2207 and IC2163

Galaxy interaction an encounter between two (or more) galaxies that is close enough for the mutual gravitational attraction to alter the appearance and, in some cases, the composition, of one or both systems. Classic examples include NGC 5195, the little, tidally distorted companion of the Whirlpool Galaxy, and the Antennae. Extreme cases of interaction result in galaxy mergers or galaxy cannibalism.

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