The Effect of Misalignment between Rotation Axis and Magnetic Field on Circumstellar Disk

TL;DR

This study uses 3D resistive magnetohydrodynamic simulations to explore how misalignment between magnetic fields and rotation axes affects circumstellar disk formation and outflows, revealing that misalignment can promote larger disks but suppress outflows.

Contribution

It provides new insights into the role of initial magnetic and rotational misalignment in disk and outflow formation during star formation, using a comprehensive set of simulations.

Findings

Misalignment promotes larger, rotationally-supported disks.

Misalignment suppresses outflow strength in moderately unstable clouds.

Highly unstable clouds show little dependence on initial angle for disk formation.

Abstract

The formation of circumstellar disks is investigated using three-dimensional resistive magnetohydrodynamic simulations, in which the initial prestellar cloud has a misaligned rotation axis with respect to the magnetic field. We examine the effects of (i) the initial angle difference between the global magnetic field and the cloud rotation axis ($\theta_0$) and (ii) the ratio of the thermal to gravitational energy ($\alpha_0$). We study $16$ models in total and calculate the cloud evolution until $\sim \! 5000$ yr after protostar formation. Our simulation results indicate that an initial non-zero $\theta_0$ ($> 0$) promotes the disk formation but tends to suppress the outflow driving, for models that are moderately gravitationally unstable, $\alpha_0 \lesssim 1$. In these models, a large-sized rotationally-supported disk forms and a weak outflow appears, in contrast to a smaller disk and strong outflow in the aligned case ($\theta_0 = 0$). Furthermore, we find that when the initial cloud is highly unstable with small $\alpha_0$, the initial angle difference $\theta_0$ does not significantly affect the disk formation and outflow driving.