CO2 from champagne bottles can form shock waves like those seen in rocket exhaust

Structures called Mach disks show up in both types of plumes

champagne cork

Gas escaping from uncorked champagne bottles can contain shock waves called Mach disks (center, top and bottom), ordinarily spotted in the supersonic exhaust of rockets and jets. Plumes from cooler bottles are bluer than those from warmer bottles.

G. Liger-Belair, D. Cordier and R. Georges/Science Advances 2019

You may not be able to blast a bottle of champagne off in the backyard, but it turns out that sparkling wine is its own kind of bottle rocket.

New high-speed videos reveal that the plume of carbon dioxide released from a popped bottle of bubbly can contain a Mach disk — a kind of visible shock wave typically seen in supersonic exhaust streams from jets and rockets. These shock waves appear when the pressure of the exhaust outflow is more than about five times as high as the surrounding air.

In champagne bottles stored at room temperature, carbon dioxide gas in the bottle’s neck is at least seven times as pressurized as ambient air. So when the bottle is uncorked, the gas that gushes out — at more than twice the speed of sound — forms a Mach disk in its plume. Within about a millisecond, the pressure inside the bottle’s throat is closer to that of the surrounding air, and the shock wave vanishes, researchers report September 20 in Science Advances.

popping champagne
When a room-temperature champagne bottle is uncorked, carbon dioxide and trace amounts of water vapor gush out at more than twice the speed of sound. Because the pressure inside the bottle’s neck is initially more than seven times as high as the pressure of the surrounding air, this gas stream can contain a fleeting Mach disk that disappears within about a millisecond.Equipe Effervescence/CNRS/Université de Reims

“The discovery of these Mach disks was a complete surprise,” says Gérard Liger-Belair, a physicist at the University of Reims Champagne-Ardenne in France. The original intent of the study, he says, was to investigate how bottle temperature affects the appearance of a champagne plume.

In experiments with champagne stored at 20° and 30° Celsius, Liger-Belair’s team confirmed previous findings that bottle temperature influences plume hue: Warmer champagne puffed out white-gray plumes, and cooler bottles exhaled deep blue.

jet plumes
Mach disks are bright bands typically seen in supersonic jet plumes where the pressure of the exhaust outflow is more than about five times as high as surrounding air. The bands appear where exhaust inside the flow has reflected off the plume–air boundary and converged back toward the center of the stream.Senior Airman Matthew Bruch/U.S. Air Force

That’s because carbon dioxide is less soluble at higher temperatures, making the gas trapped inside a 30° bottle more pressurized. When the bottles are uncorked, gas in the 30° bottle undergoes a greater pressure drop, and therefore a bigger temperature drop, than CO2 freed from the 20° bottle.

“The lower the [final] temperature, the easier the transformation” of carbon dioxide gas into dry ice, Liger-Belair says. Gas from a 30° bottle forms large ice crystals that scatter all wavelengths of visible light, giving the plume its whitish hue. Meanwhile, gas from a 20° bottle forms smaller crystals that preferentially scatter shorter, bluer wavelengths of light — similar to the way that small atmospheric molecules paint the sky blue.

Previously the staff writer for physical sciences at Science News, Maria Temming is the assistant managing editor at Science News Explores. She has bachelor's degrees in physics and English, and a master's in science writing.

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