I spent a lot of my time at work thinking about and looking at collisions. I am working on simulations of galaxy collisions and mergers, and matching simulations to data. There are a variety of ways to look at both the data and the simulations to understand what is happening. One of the most visually appealing ways to see what is happening is by watching a movie of the collision.

I’ve recently learned how to take my computer simulations of galaxy collisions and make movies out of them. My first major effort takes a simulation of a merger which computes the gravitational force between all the stars in the two galaxies to follow their motion and merger. This simulation also includes gas in the galaxies. Though they are not the dominant source of gravitational force (that is typically the dark matter), they are important for forming new stars. Also, the gas clouds can collide with other gas clouds, unlike the stars which simply fly by each other.

This video shows the gas in a merger of two galaxies (the dark matter and the stars are not shown in the video). The brightness is related to the gas density (brighter parts mean the gas density is higher):

I recently experienced another type of collision which was not quite as pleasant… I have joined an intramural softball team this summer and have been playing once a week. Last Tuesday was the first round of playoffs. I typically play 3rd base but was moved to shortstop as our regular shortstop couldn’t make the game. To make a long story short, as I was fielding a ground ball about halfway through the game and it took a wild bounce (don’t they always!) and hit me directly on the tip of my index finger. It felt like the finger was bent back and it was somewhat painful (although not painful enough that I needed to stop playing). It didn’t feel any better the next morning so I took a trip to the doctor for some X-rays:

Sure enough, the finger was broken. A plastic splint was fitted to my fingertip and I was told to leave it on for the next 6 weeks. Silver lining: I was told I can still do all my normal activities (rock climbing included!) as long as I have the splint on.

So, here’s to collisions both cosmic and close by!