Researchers in Belgium have unveiled a striking chemical reaction in which ripples along a frozen reaction front resemble the rays of a shining star. Publishing their results in Physical Review Letters, Anne De Wit and colleagues at the Université Libre de Bruxelles have shed new light on the patterns that emerge in reaction–diffusion systems, offering fresh insight into how similar structures arise in the natural world.

From forest fires to the spread of infectious diseases, many natural processes involve a “front” forming between two distinct states: be they burned and unburned forest, infected and healthy individuals, or any number of other examples in which one state spreads by consuming another.

Such behavior is often described using reaction–diffusion systems, where local reactions are coupled to transport processes such as diffusion. In the lab, this mechanism can be recreated by injecting a chemical compound into the center of a circular chamber filled with another reactant. If the chemistry is autocatalytic —where one of the reaction products catalyzes its own formation—a circular reaction front will form around the injection point.