The limit of "Ultramassive" Black Holes. There is no limit, is there? Both these links show not a limit, but a regulation that slows the growth of a black hole, due to radiating most of its food away: http://www.newscientist.com/article/dn14653-how-big-can-a-black-hole-grow.html http://www.physorg.com/news140370694.html Expansion is also stopping really big black holes from merging, but there doesn't seem to be a fundamental physical limit that I can find reference for. Can black holes increase indefinitely by merging? Could you have a 50 Septillion solar mass monster within known physics? (Not that the conditions to form it can be met) Are there any strange effects that would become evident as black holes become so massive? As far as I can tell, it would become harder and harder to identify it as a black hole at all.