The researchers say the light emitted from the snapping shrimp's bubbles suggests that the temperature inside the bubbles must be at least 5,000 degrees Kelvin (8,540 degrees Fahrenheit) at the time of collapse. Otherwise, we wouldn't see it, said Lohse.
He compared the heating inside the bubble at the time of collapse to that of a bicycle pump when it's being used to pump a tire. When you pump your bike to get air, you feel the pump is getting hot, he said. It is getting hot because you pump fast and the heat generated at compression cannot escape.
"The same thing is happening here," he added. "The bubble is compressed and getting hot on such a fast time scale that the heat cannot escape."
The researchers recorded the flash of light that occurs when a bubble collapses as well as other dim flashes of light, which are thought to be associated with bubble fragments. The mechanism responsible for the secondary flashes isn't clear.
The duration of the flash that occurs when the main bubble collapses is extremely short, lasting no longer than 10 nanoseconds and as short as 300 picoseconds, said Lohse. A picosecond is one trillionth of a second, a time scale beyond the measurement capability of the researchers' tools.
The researchers were not able to see the flashes with the naked eye. Lohse doesn't rule out, however, the possibility that they might be visible to a person very close to the shrimp when the bubble bursts and whose sight is well adjusted to the underwater darkness.
The flashes appear to have no biological significance, the researchers say, but are a by-product of the bubble collapse, which the shrimp uses to stun or kill its prey.
But light emission is nonetheless indicative of the extreme conditions inside the bubble at collapse and therefore demonstrates the violence of the event, the researchers conclude in their scientific paper.
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