Parametric Survey of Nonaxisymmetric Accretion Disk Instabilities: Magnetorotational Instability to Super-Alfvénic Rotational Instability
arXiv:2404.06925 · doi:10.3847/1538-4357/ad3d52
Abstract
Accretion disks are highly unstable to magnetic instabilities driven by shear flow, where classically, the axisymmetric, weak-field Magneto-Rotational Instability (MRI) has received much attention through local WKB approximations. In contrast, discrete non-axisymmetric counterparts require a more involved analysis through a full global approach to deal with the influence of the nearby magnetohydrodynamic (MHD) continua. Recently, rigorous MHD spectroscopy identified a new type of an ultra-localised, non-axisymmetric instability in global disks with super-Alfvénic flow. These Super-Alfvénic Rotational Instabilities (SARIs) fill vast unstable regions in the complex eigenfrequency plane with (near-eigen)modes that corotate at the local Doppler velocity and are radially localised between Alfvénic resonances. Unlike discrete modes, they are utterly insensitive to the radial disk boundaries. In this work, we independently confirm the existence of these unprecedented modes using our novel spectral MHD code Legolas reproducing and extending our earlier study with detailed eigenspectra and eigenfunctions. We calculate growth rates of SARIs and MRI in a variety of disk equilibria, highlighting the impact of field strength and orientation, and find correspondence with analytical predictions for thin, weakly magnetised disks. We show that non-axisymmetric modes can significantly extend instability regimes at high mode numbers, with maximal growth rates comparable to the MRI. Furthermore, we explicitly show a region filled with quasi-modes whose eigenfunctions are extremely localised in all directions. These modes must be ubiquitous in accretion disks, and play a role in local shearing box simulations. Finally, we revisit recent dispersion relations in the Appendix, highlighting their relation to our global framework.
References in corpus (22)
- Wind-driven Accretion in Protoplanetary Disks. I: Suppression of the Magnetorotational Instability and Launching of the Magnetocentrifugal Wind
- Black hole flares: ejection of accreted magnetic flux through 3D plasmoid-mediated reconnection
- The Stability of Magnetized Rotating Plasmas with Superthermal Fields
- Magnetohydrodynamic Instabilities in Shearing, Rotating, Stratified Winds and Disks
- Strongly magnetized accretion disks: structure and accretion from global magnetohydrodynamic simulations
- Experimental evidence for non-axisymmetric magnetorotational instability in a rotating liquid metal exposed to an azimuthal magnetic field
- Waves and Instabilities in Accretion Disks: MHD Spectroscopic Analysis
- Revisiting linear dynamics of non-axisymmetric perturbations in weakly magnetized accretion discs
- Magneto-rotational overstability in accretion disks
- Instability in strongly magnetized accretion discs: A global perspective
- Observation of axisymmetric standard magnetorotational instability in the laboratory
- A comparison of local simulations and reduced models of MRI-induced turbulence
- Identification of a non-axisymmetric mode in laboratory experiments searching for standard magnetorotational instability
- Local and global aspects of the linear MRI in accretion disks
- Saturation of the magnetorotational instability and the origin of magnetically elevated accretion discs
- Legolas: a modern tool for magnetohydrodynamic spectroscopy
- The Super-Alfvénic Rotational Instability in accretion disks about black holes
- Dissipative and nonaxisymmetric standard-MRI in Kepler disks
- Convective magneto-rotational instabilities in accretion disks
- Legolas 2.0: Improvements and extensions to an MHD spectroscopic framework
- A non-local magneto-curvature instability in a differentially rotating disk
- Robustly Unstable Eigenmodes of the Magnetoshearing Instability in Accretion Disk