  The evolution of the mass of a black hole embedded in a universe filled with
dark energy and cold dark matter is calculated in a closed form within a test
fluid model in a Schwarzschild metric, taking into account the cosmological
evolution of both fluids. The result describes exactly how accretion
asymptotically switches from the matter-dominated to the Lambda-dominated
regime. For early epochs, the black hole mass increases due to dark matter
accretion, and on later epochs the increase in mass stops as dark energy
accretion takes over. Thus, the unphysical behaviour of previous analyses is
improved in this simple exact model.
