Asked by: Roger Britton, Redruth
Although not certain, it seems very likely that most (if not all) spiral galaxies contain a supermassive black hole and sometimes more than one. That uncertainty exists for two reasons. First, we can’t physically examine every spiral galaxy in the Universe to be completely convinced of that fact. Second, theory tells us that it isn’t necessary for galaxies to contain central black holes – they will still hold together as galaxies without them.
For many galaxies, however, black holes (or rather their effects on their environments) are clearly observed in the turbulent core regions and the dynamics of their stars often indicate the presence of extremely massive objects.
There is also very strong evidence that black holes may be crucially important, perhaps even required, in the formation of galaxies in the early Universe. This would imply that indeed all types of galaxies (including spirals) contain a gravitational beast at their heart.