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As an example of a dynamical cosmological black hole, a spacetime that describes an expanding black hole in the asymptotic background of the Einstein-de Sitter universe is constructed. The black hole is primordial in the sense that it forms ab initio with the big bang singularity and its expanding event horizon is represented by a conformal Killing horizon. The metric representing the black hole spacetime is obtained by applying a time dependent conformal transformation on the Schwarzschild metric, such that the result is an exact solution with a matter content described by a two-fluid source. Physical quantities such as the surface gravity and other effects like perihelion precession, light bending and circular orbits are studied in this spacetime and compared to their counterparts in the gravitational field of the isolated Schwarzschild black hole. No changes in the structure of null geodesics are recorded, but significant differences are obtained for timelike geodesics, particularly an increase in the perihelion precession and the non-existence of circular timelike orbits. The solution is expressed in the Newman-Penrose formalism.

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It is shown that previous asymptotically Einstein–de Sitter cosmological black hole spacetimes violate the energy conditions in some region of spacetime. Thus, cosmological black hole spacetimes (for the Schwarzschild and Reissner–Nordström cases) are obtained that satisfy the energy conditions throughout spacetime. The solutions are obtained by performing conformal transformations on the isotropic forms of the isolated black hole metrics.