Kerr black holes with parity-odd scalar hair

Abstract: We study Kerr black holes with synchronised non-trivial parity-odd massive scalar hair in four dimensional asymptotically flat space-time. These axially symmetric stationary spinning solutions of the minimally coupled Einstein-Klein-Gordon theory provide yet another example of bound states in synchronous rotation with the event horizon. We discuss the properties of these parity-odd hairy black holes and boson stars and exhibit their domain of existence. Considering the ergo-regions of these hairy black holes, we show that apart from the previously discussed ergo-sphere and ergo-Saturn, they support a new type of composite ergo-surfaces with the topology of a double-torus-Saturn $(S^1\times S^1)\bigoplus(S^1\times S^1)\bigoplus S^2$.