Active vortex array in the marginal stability region

Active fluids such as dense suspensions of bacteria or sperm cells show a variety of phases ranging from disordered turbulence-like states to well-ordered vortex arrays. Continuum theories for active fluids, which belong to the class of Toner-Tu models, can be used to study such phases as well as transitions between them.
This video shows a time lapse of the the active matter system in the marginal stability region between the turbulent phase and the active vortex crystal (AVC) on a 20π x 20π domain. This marginal stability region is characterized by the intermittent melting and crystallization of the AVC. The right panel shows how the energy density changes with time.
See arxiv.org/abs/2005.06217.