Galactic tide

A galactic tide is a kind of pull felt by objects when they are near a large galaxy like our own Milky Way. This pull happens because of the strong gravitational field of the galaxy, which can stretch and squeeze things that are far away from its center.

One important thing about galactic tides is how they affect smaller galaxies that come close to a bigger one. When two galaxies move near each other, like in a galactic collision, the gravity from the bigger galaxy can pull apart smaller ones, such as dwarf or satellite galaxies.

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

Effects on external galaxies

Main article: Interacting galaxy

When two large galaxies pass close to each other, they feel strong gravitational pulls called tidal forces. These forces can stretch and shape the galaxies, creating long, curved arms of stars and gas called tidal tails. Famous examples include the Mice Galaxies and the Antennae Galaxies.

Smaller galaxies, known as satellite galaxies, orbiting larger ones can also be affected. Their shapes and movements may change, and sometimes parts of them get pulled away, forming streams of stars and gas. This process can even change how new stars form in these small galaxies. Over time, a small satellite galaxy might break apart completely, 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 affect objects far from the stars, especially in places like the Oort cloud, a huge shell of icy bodies around our Solar System. The Milky Way's gravity can stretch and squeeze this cloud, much like the Moon affects Earth’s oceans. This can send some of these icy bodies 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 that up to 90% of the comets we see might be sent toward us by these gentle galactic forces.