Global resistive MHD accretion flows around spinning AGNs: impact of resistivity on MAD state

TL;DR

This study explores how resistivity influences the dynamics and magnetic states of accretion flows around spinning supermassive black holes, revealing that resistivity affects turbulence, jet power, and the MAD state.

Contribution

It introduces a new approach to assess the magnetic state via the plasma beta parameter and compares 2D and 3D resistive MHD models around black holes.

Findings

Resistivity impacts turbulence and MRI activity in accretion flows.

MAD state occurs when average plasma beta is near or below 1.

Low-resistivity flows produce more powerful jets.

Abstract

In this study, we investigate the effect of resistivity on the dynamics of global magnetohydrodynamic accretion flows (Res-MHD) around a spinning supermassive black hole. We perform a comparative study of 2D and 3D resistive models around black holes. We examine accretion flow dynamics considering globally uniform resistivity values, ranging from $\sim 0$ to 0.1. During the simulation time of $t \lesssim 1000~t_g$, we find that the mass accretion rate is comparable for both the 2D and 3D models. However, as the flow becomes increasingly turbulent, non-axisymmetric effects begin to dominate, resulting in significant differences in the mass accretion rates between the 3D and 2D. All the resistive models in a highly magnetized flow belong to the Magnetically Arrested Disk (MAD) state. We propose an efficient and physically motivated approach to examine the magnetic state by estimating the spatial average plasma beta parameter across the computational domain. We find that when the average plasma beta is close to or below unity $( \beta_{\text{ave}} \lesssim 1 )$, the accretion flow enters the MAD state. Additionally, we find that high-resistivity flow reduces magnetorotational instability (MRI) turbulence in the accretion flow, while the turbulence structures remain qualitatively similar in low-resistivity flows. Moreover, we observe indications of plasmoid formations in low-resistivity flow compared to high-resistivity flow. Furthermore, we do not find a clear relationship between the variability of the accretion rate, magnetic flux, and resistivity. Lastly, our findings suggest that low-resistivity models produce higher power jets than those with higher resistivity.