> This was a long held theory of mine because I could not understand why a galaxy would spiral. I think in general it would be unusual if they didn’t rotate. A

> This was a long held theory of mine because I could not understand why a galaxy would spiral. I think in general it would be unusual if they didn’t rotate. Any large non-uniform mass of gas or rocks when colliding will induce some rotation. What is odd though is that for galaxies we see more of them spinning one way than another.