Boson clouds around black holes exhibit interesting physical phenomena through the Penrose process of superradiance, leading to black-hole spin-down. Axionic clouds are of particular interest, since the axion Compton wavelength could be comparable to the Schwarzschild radius, leading to the formation of “gravitational atoms” with a black-hole nucleus. These clouds collapse under certain conditions, leading to a “Bosenova.” We model the dynamics of such unstable boson clouds by a simple cellular automaton and show that it exhibits self-organized criticality. Our results suggest that the evolution through the black-hole Regge plane is due to self-organized criticality.

• Received 27 March 2012

DOI:https://doi.org/10.1103/PhysRevD.85.105022