Avalanches in a Bose-Einstein Condensate

Collisional avalanches are identified to be responsible for an 8-fold increase of the initial loss rate of a large ${}^{87}\mathrm{Rb}$ condensate. We show that the collisional opacity of an ultracold gas exhibits a critical value. When exceeded, losses due to inelastic collisions are substantially enhanced. Under these circumstances, reaching the hydrodynamic regime in conventional Bose-Einstein condensation experiments is highly questionable.