Adrian Berry's The Iron Sun (Dutton, 1977) outlines methods of using black holes to cross interstellar distances. I would also direct interested parties to read "Building The Mote In God's Eye" in the collection A Step Farther Out (Ace, 1979) by Jerry Pournelle. It is not 100% impossible to get around the light barrier. Only very very very difficult. Remember, though, it used to be impossible to fly, or go faster than sound, or go to the Moon.