Galaxies collide through gravitational interaction rather than direct stellar collisions, as space is mostly empty.

“so two galaxies colliding the Stars just pass but they definitely affect each other gravitation so this this star this star is going by it's it there's enough there is enough energy there that it can cause each to explode”

Objects interact via force fields at the atomic level without needing to physically touch.

“I'm not touching you I'm not touching you he's not touching me stop not touching me wait I we let's go a layer deeper we did a whole episode of Cosmos on this because of electromagnetic forces which hold your body together when I go up to Charles and I touch him if you actually analyze what's going ”