The ‘pop’ of a champagne cork unleashes a supersonic jet of freezing gas.
As the pressurized carbon dioxide in the neck of the bottle is released, the gas cools and condenses, forming a cloudy jet. To investigate this phenomenon in detail, Gérard Liger-Belair at the University of Reims Champagne–Ardenne in France and his colleagues used a camera that records 12,000 frames per second to film corks bursting from the necks of champagne bottles.
The footage revealed that characteristic shock waves called Mach disks form in the CO2 jet — indicating that the gas is travelling faster than the speed of sound. Mach disks are also seen in the exhaust trails of fighter jets.
The team found that changing the champagne’s temperature altered the CO2 jet’s appearance. The jet from a champagne bottle stored at 30 ºC formed large CO2 ice crystals that scattered light in a manner similar to clouds, and appeared white or grey. But ice crystals in the jet from a bottle cooled to 20 ºC were finer and preferentially scattered blue light, resulting in an evanescent blue plume.