  We study experimentally and theoretically a cold trapped Bose gas under
critical rotation, i.e. with a rotation frequency close to the frequency of the
radial confinement. We identify two regimes: the regime of explosion where the
cloud expands to infinity in one direction, and the regime where the condensate
spirals out of the trap as a rigid body. The former is realized for a dilute
cloud, and the latter for a Bose-Einstein condensate with the interparticle
interaction exceeding a critical value. This constitutes a novel system in
which repulsive interactions help in maintaining particles together.
