Can black hole superradiance be induced by galactic plasmas?

Highly spinning Kerr black holes with masses M = 1-100 M-circle dot are subject to an efficient superradiant instability in the presence of bosons with masses mu similar to 10(-10)-10(-12) eV. We observe that this matches the effective plasma-induced photon mass in diffuse galactic or intracluster environments (omega(pl) similar to 10(-10)-10(-12) eV). This suggests that bare Kerr black holes within galactic or intracluster environments, possibly even including the ones produced in recently observed gravitational wave events, are unstable to formation of a photon cloud that may contain a significant fraction of the mass of the original black hole. At maximal efficiency, the instability timescale for a massive vector is milliseconds, potentially leading to a transient rate of energy extraction from a black hole in principle as large as similar to 10(55) ergs(-1). We discuss possible astrophysical effects this could give rise to, including a speculative connection to Fast Radio Bursts. (C) 2018 The Author(s). Published by Elsevier B.V.