HOW TO CREATE A 2-DIMENSIONAL BLACK-HOLE

The interaction of a cosmic string with a four-dimensional stationary black hole is considered. If a part of an infinitely long string passe s close to a black hole it can be captured. The final stationary confi gurations of such captured strings are investigated. It is shown that the minimal 2D surface Sigma describing a captured stationary string c oincides with a principal Killing surface, i.e., a surface formed by K illing trajectories passing through a principal null ray of the Kerr-N ewman geometry. A uniqueness theorem is proved, namely, it is shown th at the principal Killing surfaces are the only stationary solutions of the string equations which enter the ergo-sphere and remain timelike and regular at the static limit surface. Geometrical properties of pri ncipal Killing surfaces are investigated and it is shown that the inte rnal geometry of Sigma coincides with the geometry of a 2D black or wh ite hole (string hole). The equations for propagation of string pertur bations are shown to be identical with the equations for a coupled pai r of scalar fields ''living'' in the spacetime of a 2D string hole. So me interesting features of the physics of 2D string holes are describe d. In particular, it is shown that the existence of the extra dimensio ns of the surrounding spacetime makes interaction possible between the interior and exterior of a string black hole; from the point of view of the 2D geometry this interaction is acausal. Possible application o f this result to the information loss puzzle is briefly discussed.