Black holes with scalar charge

Previously it had been thought that a stationary black hole with an exterior devoid of matter can be parametrized only by mass, angular momentum, and electric charge. We show here that scalar charge is also an admissible parameter. Our starting point is a new solution of Einstein's equations with stress-energy of electromagnetic and conformal scalar fields which we presented earlier. It has a black-hole geometry, and is parametrized by electric and scalar charges. Its conformal scalar field is unbounded at the event horizon, and we originally regarded this feature as incompatible with a black hole interpretation. However, following a suggestion of B. DeWitt, we show here that the infinity in the scalar field need not be physically pathological: it is not associated with an infinite potential barrier for test scalar charges; it does not cause the termination of any trajectories of these test particles at finite proper time; and it is not connected with unbounded tidal accelerations between neighboring trajectories. In view of these facts, we now regard the new solution as a genuine black hole solution