Ambipolar diffusion and the mass-to-flux ratio in turbulent collapsing clouds

Aris Tritsis (EPFL) — June 19, 2025

Abstract

Given the low ionization fraction of molecular clouds, ambipolar diffusion inevitably sets in at some stage during the star-formation process. However, computational challenges have hindered a comprehensive exploration of the effects of ambipolar diffusion in three dimensions. In this talk, I will present results from 3-dimensional non-ideal MHD chemo-dynamical simulations of turbulent collapsing molecular clouds where the resistivities are self-consistently calculated from a non-equilibrium chemical network consisting of 115 species, and with a different mean collisional rate used for each charged species in the network. These simulations reveal that, contrary to “conventional wisdom”, the features of the neutral-ion drift velocity become increasingly complex in the presence of turbulence, with many vectors even pointing outward from the cloud’s center. I will discuss the implications of this behavior for the spatial and temporal evolution of the true (i.e. differential) mass-to-flux ratio. To assess observational biases in measuring the neutral-ion drift, I have also conducted a number of non-LTE line radiative-transfer experiments and developed a roadmap to observationally constraint it. Finally, I will compare the true and observationally inferred mass-to-flux ratios, highlighting key biases and their implications.