Plumbing the abyss: black ring microstates

We construct the first smooth, horizonless "microstate geometries" that have the same charges, dipole charges and angular momenta as a BPS black ring whose horizon is macroscopic. These solutions have exactly the same geometry as black rings, except that the usual infinite throat is smoothly capped off at a very large depth. If the solutions preserve a U(1) x U(1) isometry, then this depth is limited by flux quantization but if this symmetry is broken then the throat can be made arbitrarily deep by tuning classical, geometric moduli. Interpreting these "abysses" (smooth microstate geometries of arbitrary depth) from the point of view of the AdS-CFT correspondence suggests two remarkable alternatives: either stringy effects can eliminate very large regions of a smooth low-curvature supergravity solution, or the D1-D5-P CFT has quantum critical points. The existence of solutions whose depth depends on moduli also enables us to define "entropy elevators," and these provide a new tool for studying the entropy of BPS and near-BPS black holes.