What is the effect of collision of galaxies on the planets and stars of the galaxies?
The two colliding galaxies will eventually become one over billions of years. Surprisingly, none of the stars or planets in the two galaxies will collide with each other. The two galaxies will come together to form an elliptical galaxy regardless of what they were to start with. During the collision, the galaxies will make several passes through each other, swinging around and being pulled back together by each others gravity. Many planets ans stars will be flung out into the emptiness of space but most will stay to form the new, bigger, galaxy.
