  It is shown that, in dilute-gas Bose-Einstein condensates, there exist both
dynamically stable and unstable configurations which, in the hydrodynamic
limit, exhibit a behavior resembling that of gravitational black holes. The
dynamical instabilities involve creation of quasiparticle pairs in positive and
negative energy states, as in the well-known suggested mechanism for black hole
evaporation. We propose a scheme to generate a stable sonic black hole in a
ring trap.
