Self-organization and collective migration of active condensates

Cohesive active assemblies are often regulated by spatially heterogeneous nonequilibrium driving, such as gradients in motility. Here, we show that attractive active Brownian particles (ABPs) undergo liquid-gas phase separation, and spatially varying activity fields induce emergent dynamics. Attractive active droplets migrate up activity gradients, and at sufficiently high activity, they can fragment or evaporate into a dilute phase. For finite clusters, evaporated ABPs can redistribute through the simulation box, reassemble into new clusters in lower-activity regions, and migrate again toward higher activity regions. Even in the planar-slab geometry, migration toward higher activity and activity-controlled condensate stability persist, demonstrating the generality of these effects, while the geometry determines the pathway of particle redistribution and turnover. Within this model, these dynamics arise without biochemical feedback loops and rely only on the interplay of attraction, motility, and activity gradients. Our findings show how activity gradients can regulate the spatial localization, turnover, and repeated relocation of attractive active condensates.