Of all the things to look at, I'd have to say colliding galaxies are definitely one of my favourite! This is for a few reasons...
1. It's both brutal and beautiful at the same time.
2. It's a glimpse into the future, like when Andromeda and the Milky Way will collide... This is our fate!
3. I always imagine that if there's life in the galaxies that are colliding (which I fully believe there will be), then imagine what they're seeing!
When galaxies collide it's not a sudden smash of matter, it takes hundreds of millions of years for the gravitational pull on one another to settle down into a new galaxy.
The picture below is NGC 520, a pair of interacting galaxies which started their collision 300 million years ago in the constellation Pisces. It is about 100 million light-years away and 100,000 light-years across. It's thought to be one of the brightest collisions in the sky and can be seen with a small telescope.
But how do we know it's a collision? Well, mainly because of the dust trails they leave. Much like this one with the diagonal dust trail running through it. You wouldn't see normal galaxy structures so disorganised. This one has definitely had its feathers ruffled by a fellow galaxy.