Phys. Rev. Lett. 114, 054101 (2015)

The Kepler Space Telescope has not only discovered over a thousand exoplanets, it has also found hundreds of new stellar systems — some of which are quite unusual. Take KIC 5520878, for example: it pulsates at two principal frequencies in the golden ratio. And on top of that, John Lindner and colleagues have now shown that it exhibits strange non-chaotic behaviour.

Credit: APS

In nonlinear dynamics, strange attractors usually refer to those that show an exponential sensitivity to the initial conditions, meaning that they are chaotic. Such attractors — like the famous Lorenz attractor — usually have fractal geometry. But one can also construct attractors with a fractal geometry whose dynamics are not chaotic. Called strange non-chaotic attractors (pictured), these are not mere mathematical abstractions but have been observed in experiments — albeit in rather artificial settings. Lindner et al. showed that pulsating stars are natural examples of strange non-chaotic attractors.