JIGGLE a dish of liquid slowly and steadily, and you might see stars - five or six-sided ones to be precise.
Weirdly, that's what a French team found when they made waves in a dish. How to explain it? When two or more waves interact at an angle, they can produce "nonlinear" effects, such as unusual patterns or even tsunamis. But the maths behind the causes of these waves is tricky to get right. For instance, theory predicts a variety of wave patterns from nonlinear interactions, but few have been seen.
Jean Rajchenbach's team at the University of Nice Sophia Antipolis set out to find more of these patterns by shaking silicone oil in a variety of containers. The team found the star-shaped waves in containers of different shapes and sizes, suggesting they are not affected by the shape of a container's edge. Usually, the edge affects the angle at which waves interact and so explains the shape.
The team thinks star-shaped waves shouldn't be confined to silicone oil, although the speed of the motion required and the lifetime of the waves probably depends on the viscosity of the chosen liquid. Understanding more about the new shapes may improve models of other large-amplitude waves.
The team will present their discovery next month at a meeting of the American Physical Society in San Diego, California.
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