Nuclear activity in galaxies driven by binary supermassive black holes
  Nuclear activity in galaxies is closely connected to galactic mergers and supermassive black holes (SBH). Galactic mergers perturb substantially the dynamics of gas and stellar population in the merging galaxies, and they are expected to lead to formation of supermassive binary black holes (BBH) in the center of mass of the galaxies merged. A scheme is proposed here that connects the peak magnitude of the nuclear activity with evolution of a BBH system. The scheme predicts correctly the relative fractions of different types of active galactic nuclei (AGN) and explains the connection between the galactic type and the strength of the nuclear activity. It shows that most powerful AGN should result from mergers with small mass ratios, while weaker activity is produced in unequal mergers. The scheme explains also the observed lack of galaxies with two active nuclei, which is attributed to effective disruption of accretion disks around the secondary in BBH systems with masses of the primary smaller than ~10^10 solar masses. 
Andrei P. Lobanov (Max-Planck-Institute for Radioastronomy, Bonn,   Germany)