A new instability of accretion disks around compact magnetic stars

Abstract

Aperiodic variability and Quasi Periodic Oscillations (QPOs) are observed from accretion disks orbiting white dwarfs, neutron stars, and black holes, suggesting that the flow is universally broken up into discrete blobs. We consider the interaction of these blobs with the magnetic field of a compact, accreting star, where diamagnetic blobs suffer a drag. We show that when the magnetic moment is not aligned with the spin axis, the resulting force is pulsed, and this can lead to resonance with the oscillation of the blobs around the equatorial plane; a resonance condition where energy is effectively pumped into non--equatorial motions is then derived. We show that the same resonance condition applies for the quadrupolar component of the magnetic field. We discuss the conditions of applicability of this result, showing that they are quite wide. We also show that realistic complications, such as chaotic magnetic fields, buoyancy, radiation pressure, evaporation, Kelvin--Helmholtz instability, and shear stresses due to differential rotation do not affect our results. In accreting neutron stars with millisecond periods, we show that this instability leads to Lense-Thirring precession of the blobs, and that damping by viscosity can be neglected.

Accepted for publication in the Astrophysical Journal. AASTeX LateX needed. Two figures

References in corpus (4)

• Lense-Thirring Precession and QPOs in Low Mass X-Ray Binaries
• The survival of interstellar clouds against Kelvin-Helmholtz instabilities
• A New Equilibrium for Accretion Disks Around Black Holes
• Constraints on Neutron Star Masses and Radii from Kilohertz QPOs

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• Magnetically Driven Warping, Precession and Resonances in Accretion Disks
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• Relativistic precession around rotating neutron stars: Effects due to frame-dragging and stellar oblateness
• On gravitomagnetic precession around black holes
• The ultimate outcome of black hole - neutron star mergers
• A universal relation for the propeller mechanisms in magnetic rotating stars at different scales
• Magnetic fields in AGNs and microquasars
• Lense-Thirring precession of accretion disks around compact objects
• Gamma-Ray Bursts via the Neutrino Emission from Heated Neutron Stars
• Forced oscillations in magnetized accretion disks and QPOs
• Backflows by AGN jets: Global properties and influence on SMBH accretion
• Kilohertz quasi-periodic oscillations in low mass X-ray binary sources and their relation with the neutron star magnetic field
• On the Disappearance of Kilohertz Quasi-Periodic Oscillations at a High Mass Accretion Rate in Low-Mass X-ray Binaries
• Bounds on Neutron-Star Moments of Inertia and the Evidence for General Relativistic Frame Dragging
• The iron $K_{\alpha }$ lines as a tool for magnetic field estimations in non-flat accretion flows
• Quasi Periodic Oscillations in X-ray Neutron Star and Probes of Perihelion Precession of General Relativity
• On The Low Frequency Quasi Periodic Oscillations of X-ray Sources