Space — and stop me if you’ve heard this before — is pretty big. In general, distances between objects are huge, which means collisions between objects are rare. Usually. Sometimes, objects, themselves, are pretty big, so the space between them isn’t quite the yawning gulf it is on human scales. For example, while galaxies can be millions of light years apart, the galaxies, themselves, can be hundreds of thousands of light years in size, so collisions can and do happen.