Origin of nonlinearity and plausible turbulence by hydromagnetic transient growth in accretion disks: Faster growth rate than magnetorotational instability

Abstract

We investigate the evolution of hydromagnetic perturbations in a small section of accretion disks. It is known that molecular viscosity is negligible in accretion disks. Hence, it has been argued that a mechanism, known as Magnetorotational Instability (MRI), is responsible for transporting matter in the presence of weak magnetic field. However, there are some shortcomings, which question effectiveness of MRI. Now the question arises, whether other hydromagnetic effects, e.g. transient growth (TG), can play important role to bring nonlinearity in the system, even at weak magnetic fields. Otherwise, whether MRI or TG, which is primarily responsible to reveal nonlinearity to make the flow turbulent? Our results prove explicitly that the flows with high Reynolds number (Re), which is the case of realistic astrophysical accretion disks, exhibit nonlinearity by TG of perturbation modes faster than that by modes producing MRI. For a fixed wave vector, MRI dominates over transient effects, only at low Re, lower than its value expected to be in astrophysical accretion disks, and low magnetic fields. This seriously questions (overall) persuasiveness of MRI in astrophysical accretion disks.

9 pages including 7 figures; version published in Physical Review E

References in corpus (5)

• Stability and angular-momentum transport of fluid flows between corotating cylinders
• A weakly nonlinear analysis of the magnetorotational instability in a model channel flow
• Nonmodal growth of the magnetorotational instability
• Growing hydrodynamic modes in Keplerian accretion disks during secondary perturbations: Elliptical vortex effects
• Can the viscosity in astrophysical black hole accretion disks be close to its string theory bound?

Cited by in corpus (7)

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• A pure hydrodynamic instability in shear flows and its application to astrophysical accretion disks
• Transient growth of perturbations on scales beyond the accretion disc thickness
• Origin of hydrodynamic instability from noise: from laboratory flow to accretion disk
• Forced linear shear flows with rotation: rotating Couette-Poiseuille flow, its stability and astrophysical implications
• Hydrodynamical instability with noise in the Keplerian accretion discs: Modified Landau equation
• The competition between the hydrodynamic instability from noise and magnetorotational instability in the Keplerian disks