Accretion and Diffusion Timescales in Sheets and Filaments

A comparison of accretion and (turbulent) magnetic diffusion timescales for sheets and filaments demonstrates that dense star-forming clouds generally will – under realistic conditions – become supercritical due to mass accretion on timescales at least an order of magnitude shorter than ambipolar and/or turbulent diffusion timescales. Thus, ambipolar or turbulent diffusion – while present – is unlikely to control the formation of cores and stars.