Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics

By Xue-Ning Bai. 2017

136 citations recorded by the source corpus.

The gas dynamics of weakly ionized protoplanetary disks (PPDs) are largely governed by the coupling between gas and magnetic fields, described by three non-ideal magnetohydrodynamical (MHD) effects (Ohmic, Hall, ambipolar). Previous local simulations incorporating these processes have revealed that the inner regions of PPDs are largely laminar and accompanied by wind-driven accretion. We conduct 2D axisymmetric, fully global MHD simulations of these regions (∼1–20 au), taking into account all non-ideal MHD effects, with tabulated diffusion coefficients and approximate treatment of external ionization and heating. With the net vertical field aligned with disk rotation, the Hall-shear instability strongly amplifies horizontal magnetic field, making the overall dynamics dependent on initial field configuration. Following disk formation, the disk likely relaxes into an inner zone characterized by asymmetric field configuration across the midplane, which smoothly transitions to a more symmetric outer zone. Angular momentum transport is driven by both MHD winds and laminar Maxwell stress, with both accretion and decretion flows present at different heights, and modestly asymmetric winds from the two disk sides. With anti-aligned field polarity, weakly magnetized disks settle into an asymmetric field configuration with supersonic accretion flow concentrated at one side of the disk surface, and highly asymmetric winds between the two disk sides. In all cases, the wind is magneto-thermal in nature, characterized by a mass loss rate exceeding the accretion rate. More strongly magnetized disks give more symmetric field configuration and flow structures. Deeper far-UV penetration leads to stronger and less stable outflows. Implications for observations and planet formation are also discussed.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/1b92ded2635e979b1461a5e5d38aec47ca4d6d43

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Citations in the corpus

ALMA Survey of Lupus Protoplanetary Disks. II. Gas Disk Radii (2018, background): “Such disk winds, magnetically launched from several au radii, have been theorized in non-ideal MHD models (Gressel et al. 2015), including even one-sided flows (Bai 2017), and have been observed in recent ALMA observations (Bjerkeli et al. 2016; Hirota et al. 2017).”
Pebble-isolation mass: Scaling law and implications for the formation of super-Earths and gas giants (2018, background): “Our hydrodynamical simulations do not include any turbulent motion of the gas, such as those seen in magnetohydrodynamics (MHD) simulations (Bai 2017) or in simulations with the vertical shear instability (Nelson et al. 2013; Stoll & Kley 2016).”
The Disk Substructures at High Angular Resolution Project (DSHARP). VII. The Planet–Disk Interactions Interpretation (2018, background): “…mechanisms to produce gaps and rings, such as ice lines (Zhang et al. 2015; Okuzumi et al. 2016), the dead zone transition (Pinilla et al. 2016), MHD zonal flows (Flock et al. 2015; Ruge et al. 2016), the secular GI (Takahashi & Inutsuka 2014), disk winds (Bai 2017; Suriano et al. 2018), and so on.”
Formation of planetary systems by pebble accretion and migration (2018, methodology): “This supports the use of low values of α for the midplane turbulence, without increasing the surface density of the disc Σ as 1/α (Suzuki & Inutsuka 2009; Bai 2014, 2017; Lesur et al. 2014; Gressel et al. 2015).”