http://www.physics-astronomy.com/2018/02/voracious-supermassive-black-holes-much.html#.WoxNWajiZdh
and: https://newatlas.com/alma-giant-space-donut/53421/
The mystery of cool corusus of galaxy clusters and small black holes
The Virgo and Perseus cluster have cool corusus and show unresolved 3.5 KeV radiation. The solution: In these centers only small black holes are pushed by external so called GABHs (Galaxy Anchor Black Holes) to be eaten by the giant black hole.