Galactic tide

A galactic tide is tidal force experienced by objects subject to 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 Oort cloud of the Solar System.

Origin

When one body (like the blue object in the diagrams at left) is in the gravitational field of a large mass (the yellow object), it becomes tidally distorted.

Gravitational attraction increases with decreasing distance; the closer any object A is to another object B, the more intensely A is affected by the object B's gravity, according to Newton's law of universal gravitation. This is also true of the different parts of an object; The surface of object A feels a stronger attraction to object B than the core of object A. When the other object's gravity is particularly strong, this causes the smaller object's surface to pull away from the core, and the object to distend and flatten in the direction of the larger object. The large body feels a similar but far weaker distortion caused in the same way by the gravitational field of the small body. In technical terms, the equilibrium shape of the small body is the one that minimizes its gravitational potential energy. In empty space, this would be a sphere. However, in the proximity of the large body, the lowest potential energy shape is an ovoid stretched along the axis connecting the two bodies.

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