intergalactic civilizations
It is extremely difficult to imagine how it would look a civilization far more technologically advanced than our own. Such an advanced civilization might be able to extract energy from the vacuum, they would have total control of gravity (they could create artificial gravity), so they could build artificial worlds not related to a solar system, artificial worlds that would "work" in the vast space between galaxies where there is no danger of cosmic collisions, black holes, supernovae, etc.