Sonoluminescence is the emission of short (pico-second) of light from imploding bubbles in a liquid when excited by sound. It was discovered in 1934 during sonar experiments at the University of Cologne. Light emissions are the result of the ultra-high temperatures caused as collapsing bubbles generate an imploding shock wave that compresses and heats the gas into a plasma at the centre of the bubble.
Measurements suggest extremely high temperatures - estimated to be from 2,300 K to 20,000 K.
The mechanism of sonoluminescence is unknown - though there are several as-yet-unconfirmed theories.
The two most prominent theories are currently the Shock Wave Model and the Hot-Spot model.
[…] the shock wave model that a spherical shock wave converges at the bubble center where extremely high temperature plasma is formed. The other is the hot-spot model that nearly the whole bubble is heated by quasi-adiabatic compression, where ‘quasi-‘ means appreciable thermal conduction takes place between the heated bubble interior and the surrounding liquid.
Source : Multibubble Sonoluminescence from a Theoretical Perspective Molecules 2021, 26(15), 4624
Technical details of other theories are described at Wikipedia
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