Thanatology in protoplanetary discs - The combined influence of Ohmic, Hall, and ambipolar diffusion on dead zones

By G. Lesur, Matthew W. Kunz, Sébastien Fromang. 2014

221 citations recorded by the source corpus.

Protoplanetary discs are poorly ionised due to their low temperatures and high column densities and are therefore subject to three “non-ideal” magnetohydrodynamic (MHD) effects: Ohmic dissipation, ambipolar diffusion, and the Hall effect. The existence of magnetically driven turbulence in these discs has been a central question since the discovery of the magnetorotational instability (MRI). Early models considered Ohmic diffusion only and led to a scenario of layered accretion, in which a magnetically “dead” zone in the disc midplane is embedded within magnetically “active” surface layers at distances of about 1–10 au from the central protostellar object. Recent work has suggested that a combination of Ohmic dissipation and ambipolar diffusion can render both the midplane and surface layers of the disc inactive and that torques due to magnetically driven outflows are required to explain the observed accretion rates. We reassess this picture by performing three-dimensional numerical simulations that include all three non-ideal MHD effects for the first time. We find that the Hall effect can generically “revive” dead zones by producing a dominant azimuthal magnetic field and a large-scale Maxwell stress throughout the midplane, provided that the angular velocity and magnetic field satisfy Ω·B > 0. The attendant large magnetic pressure modifies the vertical density profile and substantially increases the disc scale height beyond its hydrostatic value. Outflows are produced but are not necessary to explain accretion rates ≲ 10-7 M⊙ yr-1. The flow in the disc midplane is essentially laminar, suggesting that dust sedimentation may be efficient. These results demonstrate that if the MRI is relevant for driving mass accretion in protoplanetary discs, one must include the Hall effect to obtain even qualitatively correct results.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/7ac2514c68c9a1208678a1137e38bec6945995cc

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Citations in the corpus

Gaps, Rings, and Non-Axisymmetric Structures in Protoplanetary Disks - From Simulations to ALMA Observations (2014, background): “Recent simulations that included ambipolar diffusion (Bai & Stone 2013) and Hall diffusion (Lesur et al. 2014; Bai 2014) showed a strong laminar stress depending on the field geometry.”
Global simulations of protoplanetary disks with net magnetic flux: I. Non-ideal MHD case (2016, methodology): “This demonstrates that Hall-driven self-organization (Kunz & Lesur 2013; Béthune et al. 2016) is inefficient in stratified simulations, as already suggested by stratified shearing boxes (Lesur et al. 2014; Bai 2015).”
Ambipolar diffusion in low-mass star formation - I. General comparison with the ideal magnetohydrodynamic case (2015, background): “A better knowledge of these quantities will enable us to define more accurate initial conditions in such studies (see e.g. Lesur et al. 2014).”
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).”
GLOBAL SIMULATIONS OF PROTOPLANETARY DISKS WITH OHMIC RESISTIVITY AND AMBIPOLAR DIFFUSION (2015, methodology): “Shearing box simulations presented by Lesur et al. (2014) and Bai (2014) show that when Ω · B > 0, the Hall effect leads to the amplification of the horizontal magnetic fields within approximately two scale heights of the disk midplane, and the generation of a large scale Maxwell stress through…”
Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics (2017, background): “This is consistent with previous local simulations (Bai 2014, 2015), and for a given vertical field, the amplification factor also depends on the assumed grain abundance (e.g., see Lesur et al. 2014; Simon et al. 2015; Xu & Bai 2016 where different grain abundances are adopted).”
Accretion onto Pre-Main-Sequence Stars (2016, background): “Although the potential importance of the Hall effect in protoplanetary disks has been recognized for some time (Wardle 1999, Balbus & Terquem 2001, Kunz 2008), it has only recently been included in time-dependent numerical simulations (Lesur et al. 2014; Bai 2014, 2015; Simon et al. 2015).”