Resistive relaxation of a magnetically confined mountain on an accreting neutron star

Abstract

Three-dimensional numerical magnetohydrodynamic (MHD) simulations are performed to investigate how a magnetically confined mountain on an accreting neutron star relaxes resistively. No evidence is found for non-ideal MHD instabilities on a short time-scale, such as the resistive ballooning mode or the tearing mode. Instead, the mountain relaxes gradually as matter is transported across magnetic surfaces on the diffusion time-scale, which evaluates to ${\tau }_{\mathrm{I}}\sim 10^5-10^8$ yr (depending on the conductivity of the neutron star crust) for an accreted mass of $M_a=1.2\times 10^{-4}{M}_{\odot }$. The magnetic dipole moment simultaneously reemerges as the screening currents dissipate over ${\tau }_{\mathrm{I}}$. For nonaxisymmetric mountains, ohmic dissipation tends to restore axisymmetry by magnetic reconnection at a filamentary neutral sheet in the equatorial plane. Ideal-MHD oscillations on the Alfvén time-scale, which can be excited by external influences, such as variations in the accretion torque, compress the magnetic field and hence decrease ${\tau }_{\mathrm{I}}$ by \change{one order of magnitude} relative to its standard value (as computed for the static configuration). The implications of long-lived mountains for gravitational wave emission from low-mass X-ray binaries are briefly explored.

accepted by MNRAS

References in corpus (7)

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• Gravitational waves from mountains in newly born millisecond magnetars
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• New possible class of neutron stars: hot and fast non-accreting rotators
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• Modelling spin-up episodes in accreting millisecond X-ray pulsars
• All-sky, narrowband, gravitational-wave radiometry with folded data
• Probing the pulsar explanation of the Galactic-Center GeV excess using continuous gravitational-wave searches
• Premerger phenomena in neutron-star binary coalescences
• Gravitational waves from rapidly rotating neutron stars
• Constraining the ellipticity of millisecond pulsars with observed spin-down rates
• Does the gamma-ray binary LS I +61°303 harbor a magnetar?
• Magnetically Confined Mountains on Accreting Neutron Stars in General Relativity