What Happens When Two Galaxies Collide?

Most people think of space as a quiet, empty place. In fact, some of the most dramatic events in the universe happen on a truly enormous scale — and one of the most spectacular is when two galaxies crash into each other.

This might sound like a sudden explosion, but galaxy collisions actually happen very slowly. They can take hundreds of millions of years to complete. When two galaxies meet, their stars rarely hit each other directly, because the distances between stars are so vast. Instead, the shapes of both galaxies change completely. Gravity pulls the stars, gas, and dust into new patterns. Long streams of stars stretch out like arms, and the galaxies slowly twist around each other before eventually merging into one. This process often triggers a burst of new star formation, as clouds of gas are pushed together and begin to collapse.

Our own galaxy, the Milky Way, is actually on a collision course with our nearest large neighbour, the Andromeda Galaxy. Scientists predict this will happen in about four billion years. That sounds terrifying, but there is no need to lose sleep over it. By that point, our Sun will already be near the end of its life. Astronomers find these events fascinating rather than frightening. Studying galaxy collisions helps us understand how the universe grows and changes over time — and reminds us that even on the grandest scale, everything is always in motion.