Galactic tides

Like the earth’s oceans, the universe’s galaxies also experience Galactic tides on a larger scale. 

About the Galactic tides:

• Galactic tide is a tidal force experienced by objects subject to the gravitational field of a galaxy such as the Milky Way, the effects of which are usually confined to the immediate surroundings of the galaxy.
• When two large galaxies collide or pass near each other, they exert tidal forces, which seldom collide head-on.
• Tidal forces distort each galaxy roughly along an axis pointing toward or away from the perturbator. 
• Galactic tides create 2 arms in the galaxy, or in some cases a large tail is formed if the perturbed galaxy has the same or less mass than its colliding galaxy.
• The Andromeda galaxy, the closest galaxy to the Milky Way, has tidal streams near its edges due to the dwarf galaxies, that were later devoured. 
• Caused by: Gravitational forces within a galaxy, arising due to the interactions between celestial objects like stars and gas clouds.
• Effects:
  • It can influence various aspects of a galaxy’s evolution.
  • It can reshape a galaxy structure by creating tidal tails and bridges.
  • It can promote star formation, and disrupt smaller star systems.
  • It can disrupt the orbits of stars, leading to long-term changes in galactic structure.
  • It affects the supermassive black holes at galaxy centres, leading to events that change the ways in which they interact with nearby stars. 

Other key facts

• The Andromeda galaxy is heading towards the Milky Way galaxy at 110 km/s and will collide in 4 billion years.

Ref: Source