Since galaxies move, I guess they have to have a 'boss' which a galaxy follow...
-
When you have a traffic jam, is there one car who's the "boss"? The galaxy follows it's center of mass. The supermassive black holes is a lot of mass but it's still nothing compared to the entire galaxy. Still as the largest piece, it tends to hang around the center.
-
Yes we have found that every galaxy studied has a supermassive blackhole at its center but this is not enough to hold the galaxy together. We made a new matter called dark matter which holds the galaxies together and we know its there through the effects it has on light.
-
Yes that is what i believe is there, but it is still just a theory since you cant actually see a black hole. There is indefinitely an immense source of gravity at the center of a galaxy though.
-
we have no idea about anything to do with black holes for all we know your "supermassive" black holes could be the size of a dime, we have no idea of how physics and matter behave under those conditions