Galactic collision and dark matter

[Skaperen]

TL;DR

Galaxies could orbit each other many times. each galaxy supposedly has so much dark matter.

I have seen simulations of galactic collisions such a Andromeda and The Milky Way. How could dark matter affect such a collision, especially if an off-center collision results in one galaxy orbiting the other a few times? It seems to me that another galaxy would have an orbit much like the outer parts of the galaxy and end up orbiting at the rate the galaxy spins. each would go around the other like this at the same time; unless the dark matter gets thrown out to intergalactic space.

 

[Ibix]

Galaxies are extended objects, so two galaxies close enough to be colliding don't really have a single well-defined distance between them - the nearest edges can be touching and the farthest tens or hundreds of thousands of light years apart. That is going to lead to tidal disruption even in a grazing pass. They need to be a very long way apart to be able to orbit each other as if they were single massive points.

I'm not sure where dark matter figures into your thinking here. It'll make a difference to the interactions, sure, but not so much at the kind of qualitative level in your OP.