Cosmic Crash Unmasks Dark Matter-

There is a very interesting news report on the BBC discussing observations of black matter in the collision of two clusters of galaxy. The Hubble telescope was used for gravitational lensing to probe the distribution of the dark matter within the collision, while Chandra was used to probe the distribution of hot glowing ordinary matter. The ordinary matter heated up and slowed down in the collision, but the dark matter kept moving through, effectively fractionating away form ordinary matter. This was seen previously in the Bullet Cluster, so it is clearly a reproducible effect.
Cosmic crash
http://news.bbc.co.uk/2/hi/science/nature/7587090.stm

Does anyone know what happens when glaxies colllide, would the stars physically collide or do they pass on another harmlessly?