Three-Dimensional Simulations of Magnetized Thin Accretion Disks around Black Holes: Stress in the Plunging Region

Rebecca Shafee,Ramesh Narayan,Jeffrey E Mcclintock,Charles F Gammie,Alexander Tchekhovskoy,Jonathan C Mckinney

doi:10.1086/593148

Abstract

We describe three-dimensional general relativistic magnetohydrodynamic simulations of a geometrically thin accretion disk around a non-spinning black hole. The disk has a thickness $h/r\sim0.05-0.1$ over the radial range $(2-20)GM/c^2$. In steady state, the specific angular momentum profile of the inflowing magnetized gas deviates by less than 2% from that of the standard thin disk model of Novikov & Thorne (1973). Also, the magnetic torque at the radius of the innermost stable circular orbit (ISCO) is only $\sim2%$ of the inward flux of angular momentum at this radius. Both results indicate that magnetic coupling across the ISCO is relatively unimportant for geometrically thin disks.

Highlights

The recent development of general relativistic magnetohydrodynamic (GRMHD) codes (e.g., Gammie et al 2003; De Villiers & Hawley 2003) has allowed realistic numerical simulations of magnetized accretion disks around black holes (BHs)
In this Letter, we describe global 3D GRMHD simulations of a thin disk (h/r ∼ 0.05) around a nonspinning BH and compare our simulated model with the NT73 model
For a geometrically thin accretion disk with h/r ∼ 0.05–0.1 (Fig. 1) around a nonspinning BH, we find that the specific angular momentum profile ᐉin(r) of the accreting magnetized gas is quite similar to that assumed in the idealized model of NT73 (Fig. 2)

Summary

INTRODUCTION

The recent development of general relativistic magnetohydrodynamic (GRMHD) codes (e.g., Gammie et al 2003; De Villiers & Hawley 2003) has allowed realistic numerical simulations of magnetized accretion disks around black holes (BHs). Numerical MHD simulations by Krolik & Hawley (2002) using a pseudo-Newtonian potential, and by Krolik et al (2005) using a GRMHD code, indicated that magnetic torques are important inside the ISCO These authors found no evidence for a “stress edge,” leading them to argue that simple disk models based on the zero-torque condition (e.g., Shakura & Sunyaev 1973; Novikov & Thorne 1973, hereafter NT73) may be seriously wrong. In this Letter, we describe global 3D GRMHD simulations of a thin disk (h/r ∼ 0.05) around a nonspinning BH and compare our simulated model with the NT73 model

NUMERICAL MODEL

RESULTS

CONCLUSION