Galactic tide

A galactic tide is a pull felt by objects near a large galaxy like our Milky Way. This happens because of the galaxy's strong gravitational field. It can stretch and squeeze things far from the galaxy's center.

Galactic tides also affect smaller galaxies that come close to a bigger one. When two galaxies move near each other, the gravity from the bigger galaxy can pull apart smaller galaxies, like dwarf or satellite galaxies.

Our Solar System is affected by the Milky Way’s gravity too, especially in a faraway area called the Oort cloud. The galactic tide from the Milky Way helps shape this distant region and influences how objects move around the Sun.

Effects on external galaxies

Main article: Interacting galaxy

When two big galaxies come close to each other, they pull on each other with strong gravity. This can stretch and shape the galaxies, making long, curved arms of stars and gas called tidal tails. Famous examples are the Mice Galaxies and the Antennae Galaxies.

Smaller galaxies, called satellite galaxies, that orbit larger ones can also be changed. Their shapes and movements may shift, and sometimes parts of them get pulled away, forming streams of stars and gas. This can change how new stars are born in these small galaxies. Over time, a small satellite galaxy might break apart, leaving a trail of stars and gas around the larger galaxy.

Effects on bodies within a galaxy

See also: Oort cloud § Tidal effects

The gravity of a galaxy can change objects far from the stars, especially in places like the Oort cloud. The Oort cloud is a big shell of icy objects around our Solar System. The Milky Way's gravity can stretch and squeeze this cloud, like the Moon affects Earth’s oceans. This can send some icy objects toward the Sun, where they become comets.

The Sun’s pull is very weak in the Oort cloud, so even small changes in gravity from the galaxy can move these objects. Scientists think many of the comets we see might be sent toward us by these gentle galactic forces.