It's really hard to overstate how massive the scales are of what we see here. What looks like two celestial bodies pulverizing each other are actually clouds of billions of stars that are largely light years apart from one another. The two clouds would pass right through each other, but the gravitational changes associated with being so close together alter the trajectories of their stars and thus the shape of the galaxies.

Most stars will end up as part of a new and larger elliptical galaxy, while some stars will be thrown off into space and become permanently galaxy-less