The Nonisothermal Stage of Magnetic Star Formation. I. Formulation of the Problem and Method of Solution

TL;DR

This paper develops a comprehensive 2D model for magnetic star formation, incorporating nonideal MHD effects, detailed chemistry, and radiative transfer, to simulate the evolution of protostellar cores from diffuse clouds to dense fragments.

Contribution

It introduces a new formulation of the problem including a generalized Ohm's law and extensive chemical modeling, enhancing the realism of star formation simulations.

Findings

Accurate tracking of protostellar core evolution from 10^3 to 10^15 cm^-3 density.

Implementation of a modified Zeus-MP code with advanced physics modules.

Demonstration of the impact of nonideal MHD and radiative transfer on star formation processes.

Abstract

We formulate the problem of the formation and subsequent evolution of fragments (or cores) in magnetically-supported, self-gravitating molecular clouds in two spatial dimensions. The six-fluid (neutrals, electrons, molecular and atomic ions, positively-charged, negatively-charged, and neutral grains) physical system is governed by the radiative, nonideal magnetohydrodynamic (RMHD) equations. The magnetic flux is not assumed to be frozen in any of the charged species. Its evolution is determined by a newly-derived generalized Ohm's law, which accounts for the contributions of both elastic and inelastic collisions to ambipolar diffusion and Ohmic dissipation. The species abundances are calculated using an extensive chemical-equilibrium network. Both MRN and uniform grain size distributions are considered. The thermal evolution of the protostellar core and its effect on the dynamics are followed by employing the grey flux-limited diffusion approximation. Realistic temperature-dependent grain opacities are used that account for a variety of grain compositions. We have augmented the publicly-available Zeus-MP code to take into consideration all these effects and have modified several of its algorithms to improve convergence, accuracy and efficiency. Results of magnetic star formation simulations that accurately track the evolution of a protostellar fragment from a density ~10^3 cm^-3 to a density ~10^15 cm^-3, while rigorously accounting for both nonideal MHD processes and radiative transfer, are presented in a separate paper.