The idea of sustainable and useful desktop fusion remains a controversial field, but studies into related laboratory effects continue. Now, Ken Suslick and David Flannigan of the University of Illinois at Urbana-Champaign have demonstrated that the temperature inside a collapsing sonoluminescent bubble is four times the temperature of the surface of the sun. "When bubbles in a liquid get compressed, the insides get hot - very hot," explains Suslick, but until now nobody has measured this temperature. Sonoluminescence arises from acoustic cavitation when small gas bubbles in a liquid are "irradiated" with sound waves above 18 kHz. As the bubbles collapse intense local heating occurs, which produces light. Suslick and Flannigan observed the spectra of the light, which reveals the bubble's incredibly high temperature, and suggest that such temperatures could only arise from a plasma.