Tidal tail

A tidal tail is an elongated stream of stars and gas pulled from a galaxy by gravitational interactions, often during a close encounter or merger.

Tidal force: A differential gravitational force that arises because gravity varies across an extended object. Differences in gravity across a galaxy pull its stars and gas into a tail.
Antennae Galaxies: A pair of colliding galaxies in Corvus, named for their long tidal tails. Their prominent tails make this merger a classic example of tidal debris.
Galaxy interaction: A gravitational encounter between galaxies that changes their structures and motions. Tails provide visible evidence that galaxies have interacted.
Stellar stream: A narrow stream of stars stripped from a star cluster or dwarf galaxy by gravity. Stellar streams are usually narrower and less gas-rich than galactic tidal tails.
Galaxy merger: An interaction in which two or more galaxies collide and combine under gravity. Mergers can draw long tails from the galaxies as they pass and coalesce.
Mice Galaxies: The interacting galaxies NGC 4676, whose long tails give the pair its name. Their extended streams show tails produced by a close galactic encounter.
Dark matter halo: An extended distribution of dark matter surrounding a galaxy or galaxy cluster. Tail shapes and motions respond to the gravitational potential of the halo.
Tidal bridge: A stream of material linking two galaxies during a gravitational encounter. A bridge connects the galaxies, while a tail extends outward from one.
Orbital resonance: A condition in which orbiting bodies exert repeated gravitational influence because their orbital periods have a simple ratio. Resonant stellar orbits can concentrate material into coherent tidal features.
NGC 7252: A remnant of a galaxy merger, also known as the Atoms for Peace galaxy. Its tidal loops and tails preserve evidence of a recent merger.

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