Question: How often does a galaxy crash into another?

Jillian Scudder answered on 17 Jun 2015:

These numbers can depend a little bit on how you define your sample, but from my work we guess that about 10% of local galaxies are in some phase (which could be very early) of a collision! If you’re looking for things that are really only in the last stages of the collision, the number is much more like 2%! It’s not that often, but there are enough galaxies out there that we see them pretty commonly anyways.