This is absolutely beautiful. I'm an astronomy major and I absolutely melt when I see pictures taken from the hubble of other planets and nebulas and novas and galaxies- to me they are some of the most beautiful sights in the universe (out of everything- macro and micro). So... lol (I'm rabling now...) This is wonderful as well. I don't really have any pounters on art or anything because I have no clue how you did this, heh. If I didn't know it was fake I'd probably think it was real.
Very nice job here. I really dig the complexity and the overall feel of the whole thing.
My only criticism will have to do with the far left and right sides of the galaxy. I think they are too abrupt, and they could be softer like the front and the back. Having these sides really sharp is rather distracting.