There is a screensaver for X11 called "Galaxy." The concept is rather simple. As the screen is initialized you are presented with a number of a galaxies. These are simple clusters of pixels arranged in a disc or spiral. It approximates what we see into galaxies from here, each pixel a large cluster of stars giving off enough radiation to be visible. Each galaxy is given an initial vector upon which it begins traveling. Depending on the initial positions and vectors, you will see how they interact with each other. Often there is a collision. Sometimes there are slingshot effects. It all operates on a simplification of gravitation. Each mass on the screen affects the other masses. Sitting back and watching you are treated with a ballet of simulated stars dancing around each other, colliding, twisting along deliciously complex paths.

It's nothing fancy graphically, but the intricacies of the motion make it gorgeous. I've never seen a screen saver that was more interesting to me.

In real life, these collisions do occur. They aren't a quick dance like on the screen. When you factor in the incredible distances involved and the scope of the masses interacting the cosmic fender benders take millions if not billions of years to play out.

The beauty becomes decidedly darker when you think of the implications. I'm one that doesn't doubt the existence of life on worlds other than our own. Imagine for a moment just a single stray star going along it's merry way through the universe, shot off on a path that brushes close to our own star. The interplay of gravity on that level has the potential to rip planets out of orbit. At best, that would completely change what life could exist and how it gets by on a world. It is much more likely it would just sterilize the world completely either through freezing, collision, or melting. A slight change in orbit makes a drastic difference in climate.

Now think of that on a galactic scale. Millions of stars being shifted about, never mind all the planets, asteroids, comets, etc. How many species erased in one event? How much potential?

In perspective it's really not that dark, considering the timescales involved, species could rise and fall many times in the process. And of course, the newly shifted systems that exist after the collision may now harbor life that was not possible before.

I was reminded of all these thoughts this morning by a post on Bad Astronomy Blog. Check out Bad Astronomy's write up of some great Hubble shots of galactic collisions and interactions. As you're looking at the pretty pictures, think of all that's actually going on, and all that implies to make this eye candy.