No, there generally are not going to be colliding stars or planets. Galaxies are primarily empty space. Any location where the galactic cores intercept is a different story, and the super massive black holes of the Milky Way and Andromeda will likely devour more than a small number of stars, but aside from those specific scenarios, the chance of a star-star collision in a galactic merger is still absurdly low.
Take a handful of marbles, and have a friend take a handful of marbles, stand half a kilometer apart, and shoot them into the air towards about a 1 meter radius sphere that would be the collision space. There's a quite significant chance, with marbles, of no collisions whatsoever. Make the marbles a handful of sand and repeat it again. Compared to the galaxies that are colliding, our own is almost 500,000 light years across. The sun is not even two light seconds wide. A direct collision between two stars in that much space is incredibly unlikely.
There will be several star-star collisions, certainly, but that's attributable to the number of stars involved in a poorly coordinated interaction. In a stable galaxy, like the Milky Way is now, star-star collisions only happen with any realistic frequency between binary pairs. Even with the destabilization inherent in a galactic merger, you NEED to keep in mind how utterly LARGE a galaxy is. To scale, our entire solar system is a tiny, almost unnoticeable dot in the empty space that is our galaxy's sphere of influence.
Last edited by suomynona; Sep 5, 2013 at 03:26 AM.