Space is mostly, well, space, but that doesn't mean objects don't run into other objects. Some of the biggest collisions occur when galaxies run into other galaxies.
These events aren't uncommon, and we've seen enough of them to learn what the effects of galactic collision are. These effects can be seen in a recently released Hubble picture of spiral galaxy NGC 428.
Located 48 million light-years away in the direction of the northern hemisphere constellation Cetus, NGC 428 is something of a mess. It probably began its life as a tidy barred spiral galaxy like the Milky Way, but at some point it was disrupted by a collision with another galaxy.
NGC 428's messy shape is likely evidence of this. Its spiral structure is distorted, knocked awry by the collision. Additionally, it's forming new stars at a tremendous rate, seen in the pinkish and reddish parts of the image.
This is because when two galaxies collide their gas clouds can merge. This creates intense shocks and very hot regions of gas, the perfect breeding ground for new stars.
There are several outcomes when galaxies collide. One possibility is that the two galaxies pass through each other and continue on their way. This causes minimal disruption to the structures of both galaxies.
Another is that the two galaxies don't have enough energy to escape from each other and fall together, the smaller subsumed by the larger in a giant galactic merger. Although galaxy mergers are the most violent kind of galaxy interaction, it doesn't mean that stars collide with each other. Usually they are too far apart. Instead, molecular clouds collide, and stars are born at a tremendous rate.
Because of its distorted shape and high rate of star formation, it's highly probable NGC 428 merged with a smaller galaxy.
You can pick up some wallpaper-sized versions of this image on the Hubble website.