Universal area product for black holes: A heuristic argument

We present a heuristic argument for the universal area product: A(+)A(-) = (8 pi J)(2) + (4 pi Q(2))(2) for a four-dimensional, stationary, axisymmetric, electrically charged black hole with an arbitrary stationary axisymmetric distribution of external matter (possibly charged), derived by Marcus Ansorg and Jorg Hennig. Here A(+) and A(-) are the areas of the event and Cauchy horizons, and J and Q are the angular momentum and electric charge. Based on this argument, we conjecture that a universal area product holds for higher-dimensional, stationary, multihorizon black objects in the presence of an external stationary charged distribution of matter.