Primordial Structure of Massive Black Hole Clusters
  We describe a mechanism of the primordial black holes formation that can explain the existence of a population of supermassive black holes in galactic bulges. The mechanism is based on the formation of black holes from closed domain walls. The origin of such domain walls could be a result of the evolution of an effectively massless scalar field during inflation. The initial non-equilibrium distribution of the scalar field imposed by background de-Sitter fluctuations gives rise to the spectrum of black holes, which covers a wide range of masses -- from superheavy ones down to deeply subsolar. The primordial black holes of smaller masses are concentrated around the most massive ones within a fractal-like cluster. 
Maxim.Yu. Khlopov, Sergei.G. Rubin, Alexander.S. Sakharov