Galactic Cannibalism

Galactic cannibalism, or interacting galaxies, is a well documented phenomenon that occurs when two galaxies containing large masses pass too close to one another. The effect ranges from very minor to very major, depending on the size and proximity of the two galaxies.

Galactic cannibalism on a small scale

The most common galactic cannibalism happens when a large galaxy comes close to the spiral arm of another. Eventually, this arm begins a slow migration and is absorbed by the other, making the two galaxies appear to be connected by a tether. This focused exchange frequently causes star formation due to the sudden compression of matter. The Mice galaxies and the Whirlpool galaxy are examples of this.

Galactic cannibalism on a large scale

When galaxies collide rather than just come close, the effect is far more dramatic. Usually, this causes galactic merging when two galaxies become one. However, if either galaxy has strong momentum, the two galaxies may pass through one another intact, like two clouds passing in the sky. When this occurs, the larger galaxy usually absorbs at least part of the smaller galaxy. Galactic cannibalism, when it fully occurs, happens when these two galaxies pass and the smaller is absorbed completely by the larger, forming an irregular galaxy.

What about the Milky Way?

Some astronomers and physicists observed the movements and direction of both the Milky Way and Andromeda galaxies and surmised that the two may begin to collide within a few billion years, eventually forming one super-galaxy. Astronomers also guess that minor galactic cannibalism may be occurring between the Milky Way and Magellanic Clouds.

Galactic cannibalism is a dramatic, dynamic shift in galactic structure which occurs over hundreds of millions or billions of years. Even though the process is slow, it is an important reminder of the ever-changing nature of the universe.