The magnetic flux problem and ambipolar diffusion during star formation - One-dimensional collapse. II - Results

The magnetic flux problem lies in the observation that fluxes of typical stars are between two and five orders of magnitude smaller than fluxes of corresponding masses at interstellar densities. The detailed calculations of collapsing model clouds described in this paper show that the flux-to-mass ratio in cloud cores can decrease by two to more than four orders of magnitude in less than 10⁶yr at neutral densities n_n < 10⁹cm^-3 due to ambipolar diffusion alone. The qualitative features of the evolution (e.g., infall of the core and, often, formation of a nonmagnetic shock; initial expansion of the envelope and formation of hydromagnetic shocks; dynamical decoupling of the field from the neutral matter and reduction of the flux-to-mass ratio in the core) are common to virtually all cases which develop a rapid enough ambipolar diffusion. Clouds are studied varying in temperature from 0 to 50K; in initial central density from 10³ to 10⁶cm^-3; in initial central magnetic field from 28.9 μG to 1.7 mG; in initial half-thickness from 0.26 to 11 pc; in initial central and surface degree of ionization from 10^-7 to 10^-9 and from 10^-3 to 3×10^-5, respectively; in mass from 57 to 80,000 M_sun;.