No evidence of vorticity production from initially irrotational turbulent gravitational collapse

Gravitational collapse creates large amounts of kinetic energy that could potentially seed turbulence. If such turbulence were also suitable to initiate dynamo action, the resulting magnetic field would further modify the dynamics, especially on small length scales. However, a small-scale dynamo requires vortical turbulence, while the collapse produces mainly irrotational motions, which may not be efficient for dynamo action. Here, we study the efficiency of vorticity production during a turbulent collapse. We use a barotropic equation of state, where pressure and density gradients are parallel, and no magnetic field, so that vorticity can only be produced by viscosity. Using direct numerical simulations of gravitational collapse, we show that, for the parameter space accessible to our numerical resolution, this effect is related to the initial irrotational turbulence and is not a consequence of the collapse flow.