This is called Arp 81 (thanks to NASA’s Astronomy Picture Of The Day – http://apod.nasa.gov/apod/archivepix.html ) and it is two galaxies colliding.
Yes, that’s correct, two entire galaxies, each containing billions of stars, are colliding with each other.
The two galaxies are called NGC 6622 (left) and NGC 6621 (right).
Eventually, say in a few hundred million years, these two galaxies will become one much larger galaxy.
Fortunately for us, since they’re 280 million light-years from us, we have nothing to worry about.