Microscopy image (IMAGE) The Chinese University of Hong Kong Caption Figure: (a) Microscopy image of a giant vortex formed by the bacterial active matter. (b) Instantaneous velocity field of a giant vortex. Scale bar in a, b is 250 μm. (c) Periodic switching of the rotation direction of a giant vortex, oscillating like a torsional pendulum. (d) Phase space trajectory of an oscillatory giant vortex. Credit CUHK Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.