Reading a DC wiki (yes, wikipedias are bad...), it mentions in the Super Speed section for Kryptonians that Superman can travel at the speed of light or faster than light when in space.
I'm guessing there's been a few fights out there in the Milky Way and beyond, has Superman ever been close enough to a black hole in which he had to escape from?
I'm looking for any version of Superman from any Universe as I think, if this had ever occured, then it probably didn't happen often.