What is the True Description of Charged Black Holes?

If string theory describes nature, then charged black holes are not described by the Reissner-Nordstrøm solution. This solution must be modified to include a massive dilaton. In the limit of vanishing dilaton mass, the new solution can be found by a generalization of the Harrison transformation for the Einstein-Maxwell equations. These two solution generating transformations and the resulting black holes are compared. It is shown that the extremal black hole with massless dilaton can be viewed as the “square root” of the extremal Reissner-Nordstrøm solution. When the dilaton mass is included, extremal black holes are repulsive, and it is energetically favorable for them to bifurcate into smaller holes.