Composite black holes in external fields
  The properties of composite black holes in the background of electric or magnetic flux tubes are analyzed, both when the black holes remain in static equilibrium and when they accelerate under a net external force. To this effect, we present a number of exact solutions (generalizing the Melvin, C and Ernst solutions) describing these configurations in a theory that admits composite black holes with an arbitrary number of constituents. The compositeness property is argued to be independent of supersymmetry. Even if, in general, the shape of the horizon is distorted by the fields, the dependence of the extreme black hole area on the charges is shown to remain unchanged by either the external fields or the acceleration. We also discuss pair creation of composite black holes. In particular, we extend a previous analysis of pair creation of massless holes. Finally, we give the generalization of our solutions to include non-extreme black holes. 
R. Emparan