MRI turbulence in vertically stratified accretion discs at large magnetic Prandtl numbers

Abstract

The discovery of the first binary neutron star merger, GW170817, has spawned a plethora of global numerical relativity simulations. These simulations are often ideal (with dissipation determined by the grid) and/or axisymmetric (invoking ad hoc mean-field dynamos). However, binary neutron star mergers (similar to X-ray binaries and active galactic nuclei inner discs) are characterised by large magnetic Prandtl numbers, $\mathrm{Pm}$, (the ratio of viscosity to resistivity). $\mathrm{Pm}$ is a key parameter determining dynamo action and dissipation but it is ill-defined (and likely of order unity) in ideal simulations. To bridge this gap, we investigate the magnetorotational instability (MRI) and associated dynamo at large magnetic Prandtl numbers using fully compressible, three-dimensional, vertically stratified, isothermal simulations of a local patch of a disc. We find that, within the bulk of the disc ($z\lesssim 2H$, where $H$ is the scale-height), the turbulent intensity (parameterized by the stress-to-thermal-pressure ratio $\alpha$), and the saturated magnetic field energy density, $E_{\text{mag}}$, produced by the MRI dynamo, both scale as a power with Pm at moderate Pm ($4\lesssim \text{Pm}\lesssim 32$): $E_{\text{mag}}\sim {\text{Pm}}^{0.74}$ and $\alpha \sim {\text{Pm}}^{0.71}$, respectively. At larger Pm ($\gtrsim 32$) we find deviations from power-law scaling and the onset of a plateau. Compared to our recent unstratified study, this scaling with Pm becomes weaker further away from the disc mid-plane, where the Parker instability dominates. We perform a thorough spectral analysis to understand the underlying dynamics of small-scale MRI-driven turbulence in the mid-plane and of large-scale Parker-unstable structures in the atmosphere.

Accepted by MNRAS (17 pages + 2 pages appendices, 14 figures, 3 tables)

References in corpus (41)

• PLUTO: a Numerical Code for Computational Astrophysics
• Impact of dimensionless numbers on the efficiency of MRI-induced turbulent transport
• MHD simulations of the magnetorotational instability in a shearing box with zero net flux. I. The issue of convergence
• The Magnetic Rayleigh-Taylor Instability in Three Dimensions
• Angular Momentum Transport in Accretion Disks: Scaling Laws in MRI-driven Turbulence
• On the Magnetic Prandtl Number Behavior of Accretion Disks
• Convection Causes Enhanced Magnetic Turbulence in Accretion Disks in Outburst
• High accretion rates in magnetised Keplerian discs mediated by a Parker instability driven dynamo
• Viscous, Resistive Magnetorotational Modes
• Long-term evolution of neutron-star merger remnants in general relativistic resistive-magnetohydrodynamics with a mean-field dynamo term
• The Role of Disk Winds in the Evolution and Dispersal of Protoplanetary Disks
• Viscous evolution of a massive disk surrounding stellar-mass black holes in full general relativity
• Surface Structure in an Accretion Disk Annulus with Comparable Radiation and Gas Pressure
• Evidence for an emerging disc wind and collimated outflow during an X-ray flare in the narrow-line Seyfert 1 galaxy Mrk 335
• The fundamental difference between shear alpha viscosity and turbulent magnetorotational stresses
• Local models of astrophysical discs
• Angular momentum transport and large eddy simulations in magnetorotational turbulence: the small Pm limit
• Evolution of a Relativistic Outflow and X-ray Corona in the Extreme Changing-Look AGN 1ES 1927+654
• MRI-driven $\alpha -\Omega$ dynamos in protoneutron stars
• On the nature of the magnetic Rayleigh-Taylor instability in Astrophysical Plasma: The case of uniform magnetic field strength
• On the convergence of Magnetorotational turbulence in stratified isothermal shearing boxes
• Gravito-turbulence and the excitation of small-scale parametric instability in astrophysical discs
• Implementation of advanced Riemann solvers in a neutrino-radiation magnetohydrodynamics code in numerical relativity and its application to a binary neutron star merger
• Magnetorotational instability and dynamo action in gravitoturbulent astrophysical discs
• Dissipative effects on the sustainment of a magnetorotational dynamo in Keplerian shear flow
• Magnetorotational dynamo chimeras. The missing link to turbulent accretion disk dynamo models?
• Impact of convection and resistivity on angular momentum transport in dwarf novae
• Nonlinear transverse cascade and two-dimensional magnetohydrodynamic subcritical turbulence in plane shear flows
• Magnetorotational instability: nonmodal growth and the relationship of global modes to the shearing box
• MRI-driven dynamo at very high magnetic Prandtl numbers
• Zero net flux MRI-turbulence in disks $-$ sustenance scheme and magnetic Prandtl number dependence
• MRI turbulence in accretion discs at large magnetic Prandtl numbers
• Microphysical dissipation, turbulence and magnetic fields in hyper-accreting discs
• Nonlinear transverse cascade and sustenance of MRI-turbulence in Keplerian disks with an azimuthal magnetic field
• On characterizing nonlocality and anisotropy for the magnetorotational instability
• Assessment of a new sub-grid model for magneto-hydrodynamical turbulence. I. Magnetorotational instability
• Sustained Turbulence in Differentially Rotating Magnetized Fluids at Low Magnetic Prandtl Number
• Finite-time response of dynamo mean-field effects in magnetorotational turbulence
• Dynamics of magnetic flux tubes in accretion discs of T Tauri stars
• Magnetohydrodynamic convection in accretion discs
• The Low Temperature Corona in ESO 511$-$G030 Revealed by NuSTAR and XMM-Newton

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