![]() While a large tail is formed if the perturbed galaxy is equal to or less massive than its partner, if it is significantly more massive than the perturbing galaxy, then the trailing arm will be relatively minor, and the leading arm, sometimes called a bridge, will be more prominent. Just as the Moon raises two water tides on opposite sides of the Earth, so a galactic tide produces two arms in its galactic companion. Two very prominent examples of collisions producing tidal tails are the Mice Galaxies and the Antennae Galaxies. ![]() The stars and gas that comprise the tails will have been pulled from the easily distorted galactic discs (or other extremities) of one or both bodies, rather than the gravitationally bound galactic centers. If a tail appears to be straight, it is probably being viewed edge-on. Such tails are typically strongly curved. As the two galaxies briefly orbit each other, these distorted regions, which are pulled away from the main body of each galaxy, will be sheared by the galaxy's differential rotation and flung off into intergalactic space, forming tidal tails. Two interacting galaxies will rarely (if ever) collide head-on, and the tidal forces will distort each galaxy along an axis pointing roughly towards and away from its perturber. Two large galaxies undergoing collisions or passing nearby each other will be subjected to very large tidal forces, often producing the most visually striking demonstrations of galactic tides in action. Tidal forces are dependent on the gradient of a gravitational field, rather than its strength, and so tidal effects are usually limited to the immediate surroundings of a galaxy. Main article: Interacting galaxy Galaxy collisions The lengthy tidal tails of the colliding Antennae Galaxies
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