"Galaxies, on the other hand, will sail on through, rarely actually "colliding" in the way you may think because of the large spaces within stars and other objects within them."
Is that correct? I was under the impression that galaxies that "collide" will "merge" instead of "pass through each other".
Yes, few stars will actually collide with each other, but the billions-body gravitational interaction will definitely affect the trajectories of the stars in both galaxies.
And, if the gas has a substantial fraction of the galaxies' masses, then the stars and central black holes will be gravitationally attracted to that, too.
So, what exactly is expected to just "pass through" other than maybe the "dark matter" and only if it has a low enough cross section for self interaction?