Abstract
Low-energy, near-horizon scaling limits of black holes which lead to string theory on AdS2 × S2 are described. Unlike the higher-dimensional cases, in the simplest approach all finite-energy excitations of AdS2 × S2 are suppressed. Surviving zero-energy configurations are described. These can include tree-like structures in which the AdS2 × S2 throat branches as the horizon is approached, as well as disconnected AdS2 × S2 universes. In principle, the black hole entropy counts the quantum ground states on the moduli space of such configurations. In a nonsupersymmetric context AdSD for general D can be unstable against instanton-mediated fragmentation into disconnected universes. Several examples are given.