Giant hole and circular superflow in a fast rotating Bose-Einstein   condensate
  A fast rotating Bose-Einstein condensate confined in a quadratic-plus-quartic potential is found to dynamically generate a "giant vortex" that absorbs all phase singularities into a central low density hole, thereby sustaining a quasi-one-dimensional circular superflow at a supersonic speed. 
Kenichi Kasamatsu, Makoto Tsubota, and Masahito Ueda