Cosmological coupled black holes immersed in dark sector

Abstract: Motivated by theoretical and observational developments of cosmological coupled black holes, we construct an exact analytical solution for a black hole immersed in an anisotropic dark sector background, adopting the framework established by [Cadoni et al., JCAP 03 (2024) 026]. By generalizing a static seed metric to a dynamical FLRW background, we derive a solution where the black hole mass co-evolves with the cosmic expansion. We then obtain the explicit form of the radius-dependent coupling exponent, revealing that the interaction is governed by the dark halo profile. Considering the ubiquity of the dark halos surrounding supermassive black holes, our model provides a potential realization of cosmological coupling, interpreting the mass growth as the dynamical response of the surrounding dark sector fluid to the Hubble flow, distinct from the method of modifying the black hole's internal equation of state.