We saw some video clips that simulate these interactions they are available here. Basically, we see the interaction destroying the spiral structure . Long tails of stars can result, and the galaxies merge. Collisions destroy spiral structure , and the result of two or three or more mergers may be an elliptical galaxy . At the hearts of rich galaxy clusters, there can be expected to be many collisions and mergers this may be the origin of the giant elliptical galaxies that are there.
Collisions stimulate a burst of star formation .
We can see evidence for this in interacting galaxies. But after the burst, all the gas which is the fuel for forming stars, is used up. So that may be why elliptical galaxies tend to have all old stars their gas and dust was used up back when they were interacting galaxies. Galactic cannibalism may contribute to the formation of irregular galaxies. If a small galaxy interacts with a large galaxy, the large galaxy may escape unscathed, but the small galaxy may be torn apart .