Researchers from the University of Illinois at Urbana-Champaign reported in the Oct. 21 issue of Nature that the temperature of imploding bubbles reaches thousands of degrees kelvin. Scientists studying cavitation by ultrasonic stimulation had predicted the intense temperatures, but the team is the first to test the theories by observation. The researchers used a spectrograph to analyze the luminescence that accompanies acoustic cavitation. High-resolution spectra of the emissions of Cr(CO)6 and Mo(CO)6 bubbles were collected and compared with lower-resolution spectra. The relative intensities of the spectra indicated temperatures as high as 5200 K, dependent on such factors as the vapor pressure on the solvent.