Dissipation and vortex creation in Bose-Einstein condensed gases

We solve the Gross-Pitaevskii equation to study energy transfer from an oscillating ``object'' to a trapped Bose-Einstein condensate. Two regimes are found: for object velocities below a critical value, energy is transferred by excitation of phonons at the motion extrema; while above the critical velocity, energy transfer is via vortex formation. The second regime corresponds to significantly enhanced heating, in agreement with a recent experiment.