Tidal tail

A tidal tail is a thin, elongated region of stars and interstellar gas that extends into space from a galaxy.

Tidal tails occur as a result of galactic tide forces between interacting galaxies.

Most tidal tails are slightly curved due to the rotation of the host galaxies.

[4] Several astrophysicists expressed their doubts that these extensions could occur solely as the result of tidal forces,[5][6] including Zwicky himself, who described his own views as "unorthodox".

However, in 1972, renowned astronomer Alar Toomre proved that it was indeed tidal forces that were responsible for the tails.