Sonoluminescence is the phenomenon which occurs when a bubble in water collapses to produce light and heat. These bubbles can reach temperatures similar to the heat of the surface of the Sun.
To create sonoluminescence there has to be sound with the right frequency, moving through water. There is a species of shrimp, known as Mantis Shrimp, that creates sonoluminescence as a defense mechanism.
Sound waves are molecules that oscillate, creating areas of higher and lower pressure. When sound moves through water, the water can be pulled a part enough that the areas of low pressure create a small bubble of water vapor, which is a process called “cavitation.”
Cavitation bubbles are different from regular bubbles, because cavitation literally tears a gap in the water, instead of gas being released underwater. Because the low air pressure, the cavitation bubbles collapse.
As the walls of the bubble get smaller, the pressure rapidly increases, causing temperatures to rise. When the bubble gets hotter multiple chemical reactions occur, and all the molecules react with each other which may release energy and cause a small burst of light.
It is also possible that the gas inside the bubble is briefly turning into plasma, releasing light, then turning back into gas.