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17 Jun 2002
Sonoluminescence, the puzzling glow emitted by a bubble in a field of high-pitched sound waves, may be caused by a tiny jet of liquid that shoots across the interior of the bubble at supersonic speed and slams into the opposite side, a Johns Hopkins researcher has proposed. At the point where this powerful jet strikes the bubble wall, it "fractures" the liquid, releasing energy in the form of light, says Andrea Prosperetti, an internationally respected expert on the mechanical properties of bubbles.
Prosperetti's theory offers an alternative to the widely held view that the bubble glows because of shock waves that concentrate energy in its center as it shrinks. His theory also deflates the hope among some researchers that sonoluminescence generates enough pressure and heat to produce nuclear fusion, a potential source of cheap, clean energy. Some scientists have speculated that bubble temperatures during sonoluminescence exceed 2 million degrees Fahrenheit, near the levels needed for fusion.
But it Prosperetti's theory holds true, the heat inside the bubbles would peak at about 10,000 degrees F, the level found at the sun's surface. "It's enough to explain the chemical activity, but it's far below the amount needed to produce nuclear fusion," says Prosperetti, who is the Charles A. Miller, Jr. Distinguished Professor of Mechanical Engineering at Hopkins.
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