colliding may lead to merging if two galaxies collide and do not have enough momentum to continue traveling after the collision. in that case, they fall back into each other and eventually merge into one galaxy after many passes through each other. if one of the colliding galaxies is much larger than the other, it will remain largely intact after the merger. the larger galaxy will look much the same, while the smaller galaxy will be stripped apart and become part of the larger galaxy. when galaxies pass through each other, unlike during mergers, they largely retain their material and shape after the pass.