Asymmetric evolution of magnetic reconnection in collisionless accretion disk

TL;DR

This study uses hybrid simulations to explore asymmetric magnetic reconnection in collisionless accretion disks, revealing how Hall effects and differential rotation influence magnetic structures and turbulence.

Contribution

It introduces a hybrid simulation approach to analyze asymmetric magnetic reconnection and its coupling with MRI in accretion disks, highlighting the role of X-point migration and magnetic field enhancement.

Findings

Asymmetric out-of-plane magnetic field structures during reconnection.

X-point migration direction depends on initial current and rotation.

Enhanced perpendicular magnetic field linked to MRI-reconnection coupling.

Abstract

An evolution of a magnetic reconnection in a collisionless accretion disk is investigated using a 2.5 dimensional hybrid code simulation. In astrophysical disks, magnetorotational instability (MRI) is considered to play an important role by generating turbulence in the disk and contributes to an effective angular momentum transport through a turbulent viscosity. Magnetic reconnection, on the other hand, also plays an important role on the evolution of the disk through a dissipation of a magnetic field enhanced by a dynamo effect of MRI. In this study, we developed a hybrid code to calculate an evolution of a differentially rotating system. With this code, we first confirmed a linear growth of MRI. We also investigated a behavior of a particular structure of a current sheet, which would exist in the turbulence in the disk. From the calculation of the magnetic reconnection, we found an asymmetric structure in the out-of-plane magnetic field during the evolution of reconnection, which can be understood by a coupling of the Hall effect and the differential rotation. We also found a migration of X-point whose direction is determined only by an initial sign of J_0 \times \Omega_0, where J_0 is the initial current density in the neutral sheet and \Omega_0 is the rotational vector of the background Keplerian rotation. Associated with the migration of X-point, we also found a significant enhancement of the perpendicular magnetic field compared to an ordinary MRI. MRI-Magnetic reconnection coupling and the resulting magnetic field enhancement can be an effective process to sustain a strong turbulence in the accretion disk and to a transport of angular momentum.