Multi-armed vortices in an active chemical medium

Abstract

An excellent example of self-organization in nonequilibrium systems^1,2 is the origination of rotating spiral vortices. These vortices have been observed in a wide range of active media—in the morphogenesis processes of social amoeba Dictyostelium discoideum^3,4, in cardiac muscle during some arrhythmias⁵ and in the Belousov–Zhabotinsky reaction^6–9. All these vortices are simple spirals. The rotating structures of a higher order of symmetry such as multiarmed vortices have not previously been observed experimentally. We have obtained two-, three- and four-armed rotating spiral vortices in an active chemical medium. These structures were appreciably stable and we observed their rotation for more than half an hour, which was in striking contrast to unstable multiple vortices in many other physical systems (such as superfluid ⁴He or superconductors^10,11).