Motility-induced phase separation in an active dumbbell fluid

We study a suspension of active dumbbells of variable density, as a minimal example of an active polar fluid. As in a fluid of spherical swimmers, we find that motility triggers a nonequilibrium phase separation if the density exceeds a critical threshold. We also show that the phase separation is lost when the active force becomes too large, ultimately due to inertial effects. Remarkably, the aggregates which assemble spontaneously break chiral symmetry and rotate; they also display a nematic ordering with spiral patterns.