  We study the onset of bubble formation (cavitation) in the quark-gluon plasma
as a result of the reduction of the effective pressure from bulk-viscous
corrections. By calculating velocity gradients in typical models for
quark-gluon plasma evolution in heavy-ion collisions, we obtain results for the
critical bulk viscosity above which cavitation occurs. Since present
experimental data for heavy-ion collisions seems inconsistent with the presence
of bubbles above the phase transition temperature of QCD, our results may be
interpreted as an upper limit of the bulk viscosity in nature. Our results
indicate that bubble formation is consistent with the expectation of
hadronisation in low-temperature QCD.
