What happens when galaxies collide?
It is likely that you have seen many clusters of stars that get quite close together on many star maps before. While many of these items on a star map are actually millions of light years away from each other there are some occasions in the history of our universe were galaxies will collide.
Galaxy interaction is more common than you may think and mergers between galaxies are considered to be some the greatest evolutionary forces in our universe. As the average galaxy is made up of over 100 billion stars the direct collision between two galaxies actually causes very little issues with relation to stars colliding.
The density of stars in a galaxy may look extremely close in some of the astronomical photos that we have taken with various space telescopes. The average distance between the stars however is extremely large in this means that a head-on collision between stars is virtually impossible. As stars are mostly created using gases theoretically if do stars were to collide it also would only make them pass through each other without much effect.
The interaction between various galaxies manipulates the flow of gas and dust. The interaction gravitationally can cause various material from each galaxy to disrupt the morphology. Shock waves also occurred due to the friction between gases in the galaxies as it is moving in different directions. Through several past events we have logged quick snapshots of these interactions. There's also some computer simulations available of what happens when galaxies collide. It's overly quite an unpredictable process but the merging process can create some exciting evolutionary bounds for both participants!