From SPACE.com:

A galaxy in Stephan’s Quintet is rushing headlong into a cluster of neighboring galaxies at more than one million mph and generating one of the largest shock waves scientists have ever seen.

The finding, made using NASA’s Spitzer Space Telescope, gives astronomers a chance to see a galactic collision in action…

The shock wave created by the approaching galaxy, called a “bow shock” and akin to that generated ahead of a boat moving through water, is actually larger than our own Milky Way galaxy.  That should give you an idea of the cosmic scale of such collisions.