Resistive Collapse of 2D Non-rotating Magnetized Isothermal Toroids: Formation of Pseudodisks

TL;DR

This study investigates the collapse of magnetized isothermal toroids, revealing how magnetic diffusivity influences pseudodisk formation, structure, and dynamics, with implications for star formation and observable envelope properties.

Contribution

It provides a detailed analysis of pseudodisk formation under non-ideal MHD conditions, highlighting the role of magnetic diffusivity and improved resolution in collapse simulations.

Findings

Pseudodisks form across all magnetization levels and diffusivities.

Magnetic diffusivity affects pseudodisk size, structure, and magnetic support.

Field line structures become less radial with explicit Ohmic diffusivity.

Abstract

The collapse of singular magnetized toroids (Li & Shu 1996) is a natural representation of an early phase in star formation, bridging the prestellar and protostellar phases of the collapse of molecular cloud cores. We revisit the collapse study of Allen et al. (2003b), now with explicit nonideal MHD (Ohmic diffusivity $\eta$) and higher resolution using a code able to cover a broader range of the magnetization parameter $H_0$. Galli-Shu equatorial pseudodisks form for all values of $H_0$ and $\eta$, and the asymptotic central mass growth rate is in the scale $\dot{M}_*\sim(a^3/G)(1+H_0)$, where $a$ is the isothermal sound speed, consistent with previous results and predictions. The explicit Ohmic diffusivity makes the field line structure less radial than in previous work, connecting the pseudodisk more effectively to its surroundings. Matter can fall efficiently onto the pseudodisk surfaces, forming oblique shocks, where shock heating and large density gradients raise the possibility of rich astrochemistry. Pseudodisk size and structure are influenced by magnetic diffusivity. Force and velocity ratios were computed to explore the magnetic support within the pseudodisk and its induced slowdown in infall velocity. Magnetic diffusivity was measured to control the strength of these effects and their location within the pseudodisk. The dependence of the field line configurations, pseudodisk structure, and velocity ratios on magnetic diffusivity has observable consequences for collapsing envelopes.