INTERACTING GALAXIES – WHAT TO EXPECT WHEN YOU’RE EXPECTING
In case you haven’t heard by now – in approximately 3 to 5 billion years our galaxy, the Milky Way, is expected to collide with the Andromeda galaxy! It sounds dramatic, and it is, though perhaps not in the way you had initially thought…
Colliding, or interacting, galaxies are very common in the universe as we have observed it. Scientists are actually considering the thought that the merging of galaxies is one of the main causes of the evolution of a galaxy.
It should be noted, however, that not all galaxies that come close actually merge. There have been observed instances where they may pass by each other, or smaller galaxies orbiting larger ones, such as the case with Andromeda – the very same galaxy that may merge with our own.
Even if the two did merge, the possibility is almost 0 that two stars would collide when the galaxies interact. Galaxies are big – really big, so there’s plenty of moving room for all those merging stars and planets. There’s even enough room for all the new star formations that are common when the gas and dust in the space between collide.
Whether they merge or simply pass by each other, these occurrences often mean for changes in the formation of the galaxy, or galaxies as the case may be. When passing each other, the gravity of one may pull on the other to alter its shape completely. Or, two larger spiral galaxies can merge to form an elliptical galaxy, while smaller ones will usually create a bigger spiral galaxy.
In fact, the Milky Way is a large spiral galaxy which has merged with smaller galaxies in the past, and is merging with a dwarf galaxy now.
The total number of galaxies ours has merged with is unknown, though it is not estimated to be too large of a number due to the spiral nature of our galaxy and how intact it is. Andromeda, too, is a large spiral galaxy.
You may be wondering,” If the universe is expanding why are galaxies colliding?” The short answer is gravity. It causes the galaxies to want to merge, but the expansion of the universe pulls them apart. Galaxies that are closer are more likely to win the battle of gravity vs. expansion and merge, which is why it is predicted that the Milky Way and Andromeda galaxies will merge in the future.