Advection of Magnetic Fields in Accretion Disks: Not So Difficult After All

Abstract

We show that a large-scale, weak magnetic field threading a turbulent accretion disk tends to be advected inward, contrary to previous suggestions that it will be stopped by outward diffusion. The efficient inward transport is a consequence of the diffuse, magnetically-dominated surface layers of the disk, where the turbulence is suppressed and the conductivity is very high. This structure arises naturally in three-dimensional simulations of magnetorotationally unstable disks, and we demonstrate here that it can easily support inward advection and compression of a weak field. The advected field is anchored in the surface layer but penetrates the main body of the disk, where it can generate strong turbulence and produce values of alpha (i.e., the turbulent stress) large enough to match observational constraints; typical values of the vertical magnetic field merely need to reach a few percent of equipartition for this to occur. Overall, these results have important implications for models of jet formation which require strong, large-scale magnetic fields to exist over a region of the inner accretion disk.

13 pages, 4 figures; accepted for publication in The Astrophysical Journal (v2: added references to papers by McKinney et al.)

References in corpus (8)

• Accretion disc viscosity: how big is alpha?
• MHD simulations of the magnetorotational instability in a shearing box with zero net flux. I. The issue of convergence
• Angular Momentum Transport in Accretion Disks: Scaling Laws in MRI-driven Turbulence
• Global MHD simulations of stratified and turbulent protoplanetary discs. I. Model properties
• Disk-Jet Coupling in Black Hole Accretion Systems I: General Relativistic Magnetohydrodynamical Models
• Empirical relation between angular momentum transport and thermal-to-magnetic pressure ratio in shearing box simulations
• Large Scale B-Field in Stationary Accretion Disks
• Thermodynamics of an Accretion Disk Annulus with Comparable Radiation and Gas Pressure

Cited by in corpus (21)

• Evolution of Protoplanetary Discs with Magnetically Driven Disc Winds
• Transition from Regular to Chaotic Circulation in Magnetized Coronae near Compact Objects
• Hall-effect Mediated Magnetic Flux Transport in Protoplanetary Disks
• Black-hole jets without large-scale net magnetic flux
• Advection/Diffusion of Large-Scale B-Field in Accretion Disks
• Magnetic outflows from turbulent accretion disks: I. Vertical structure & secular evolution
• Global evolution of the magnetic field in a thin disc and its consequences for protoplanetary systems
• Corotational Instability of Inertial-Acoustic Modes in Black Hole Accretion Discs and Quasi-Periodic Oscillations
• Grand challenges in protoplanetary disc modelling
• Magnetic layers and neutral points near rotating black hole
• Magnetic-Field Structure in the Accretion Disks of Semi-Detached Binary Systems
• Winds and Disk Turbulence Exert Equal Torques on Thick Magnetically Arrested Disks
• Magnetic field transport in compact binaries
• Viscous Driving of Global Oscillations in Accretion Discs Around Black Holes
• Local semi-analytic models of magnetic flux transport in protoplanetary discs
• Launching and Quenching of Black Hole Relativistic Jets at Low Accretion Rate
• Global magnetohydrodynamic simulations of the inner regions of protoplanetary discs. I. Zero-net flux regime
• Radiation intensity and polarization in atmosphere with chaotic magnetic field
• Inertial-Acoustic Oscillations of Black-Hole Accretion Discs with Large-Scale Poloidal Magnetic Fields
• Global Non-ideal Magnetohydrodynamic Simulations of Protoplanetary Disks with Outer Truncation
• The dependence of the fraction of radio luminous quasars on redshift and its theoretical implications