Emergent comet-like swarming of optically driven thermally active colloids

We propose a simple system of optically driven colloids that convert light into heat and move in response to self- and collectively- generated thermal gradients. We show that the system exhibits self-organization into a moving comet-like swarm and characterize the structure and response of the swarm to a light intensity dependent external tuning parameter. We observe many interesting features in this nonequilibrium system including circulation and evaporation, intensity-dependent shape, density and temperature fluctuations, and ejection of hot colloids from the swarm tip.