Hydrodynamic Instability of a Chiral Active Fluid

We study the collective dynamics of spinning colloidal magnets suspended in water. When they spin, these particles attract and form a cohesive material that behaves like a fluid. We probe, experimentally, the fluid dynamics of this two-dimensional magnetic gyrofluid. In particular, we find that, under certain conditions, it can undergo a hydrodynamic instability that causes it to break up into droplets. We investigate this instability, and we use a hydrodynamic model to understand its origin.