  A Bose-Einstein condensate of cold atoms is a superfluid and thus responds to
rotation of its container by the nucleation of quantized vortices. If the
trapping potential is su ciently strong, there is no theoretical limit to the
rotation frequency one can impose to the fluid, and several phase transitions
characterized by the number and distribution of vortices occur when it is
increased from zero to infinity. In this note we focus on a regime of very
large rotation velocity where vortices disappear from the bulk of the fluid,
gathering in a central hole of low matter density induced by the centrifugal
force.
