2017/01/31 by Zhaohuan Zhu, James M. Stone · 160 citations
Physics and Astronomy · #Accretion (finance) #Angular momentum #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Corona (planetary geology) #Flux (metallurgy) #Intermediate polar #Magnetic field #Magnetic flux #Magnetohydrodynamics #Stellar, planetary, and galactic studies #Thermal wind #Turbulence #astro-ph.EP
paper · pdf · doi:10.3847/1538-4357/aaafc9
published in The Astrophysical Journal 857(1), 34 (IOP Publishing) · Two additional figures, accepted by the AAS Journals
openalex created_date 2017/01/26 · arxiv created 2018/02/15 · openalex publication_date 2018/04/10 · arxiv updated 2018/04/25 · openalex updated_date 2026/08/05
Abstract We report results from global ideal MHD simulations that study thin accretion disks (with thermal scale height H / R = 0.1 and 0.05) threaded by net vertical magnetic fields. Our computations span three orders of magnitude in radius, extend all the way to the pole, and are evolved for more than 1000 innermost orbits. We find that (1) inward accretion occurs mostly in the upper magnetically dominated regions of the disk at z ∼ R , similar to predictions from some previous analytical work and the “coronal accretion” flows found in GRMHD simulations. (2) A quasi-static global field geometry is established in which flux transport by inflows at the surface is balanced by turbulent diffusion. The resulting field is strongly pinched inwards at the surface. A steady-state advection–diffusion model, with a turbulent magnetic Prandtl number of order unity, reproduces this geometry well. (3) Weak unsteady disk winds are launched beyond the disk corona with the Alfvén radius R A / R 0 ∼ 3. Although the surface inflow is filamentary and the wind is episodic, we show that the time-averaged properties are well-described by steady-wind theory. Even with strong fields, β 0 = 10 3 at the midplane initially, only 5% of the angular momentum transport is driven by the wind, and the wind mass flux from the inner decade of the radius is only ∼0.4% of the mass accretion rate. (4) Within the disk, most of the accretion is driven by the Rϕ stress from the MRI and global magnetic fields. Our simulations have many applications to astrophysical accretion systems.