I would like to ask where the greatest density of mass per area could be in the universe. I don't mean like "next to a black hole" but as in a highly densely populated area of space. I would naturally think it would have to be in a supercluster of galaxies, as compared to a void. Now within a supercluster we have galaxy groups. Would you agree that one of the densest regions in space is that of a galaxy group within a supercluster?