Vortex formation of spherical self-propelled particles around a circular obstacle

Area of Science:

• Physics
• Soft Matter Physics
• Active Matter Physics

Background:

• Vortices are common in active systems, often arising from broken spatial symmetry.
• Symmetry breaking typically involves asymmetric shapes, collective motion, hydrodynamic interactions, or alignment effects.

Purpose of the Study:

• To investigate the spontaneous formation of vortices in a simplified active matter system.
• To understand the underlying mechanisms of symmetry breaking and vortex sustainment without external factors.

Main Methods:

• Computational simulations were employed.
• The model system consisted of spherical self-propelled particles interacting with a circular obstacle.

Main Results:

• A vortex spontaneously formed around the circular obstacle under specific conditions.
• Vortex formation was dependent on high particle activity (persistence) and a limited range of obstacle sizes.
• The vortex sustainment was attributed to biased particle acceptance around the obstacle based on propulsion direction.

Conclusions:

• Demonstrates spontaneous symmetry breaking in active matter systems.
• Provides new insights into vortex formation and ratchet phenomena in the absence of conventional symmetry-breaking mechanisms.