Journal Article

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

M. Vigelius and A. Melatos

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 395, issue 4, pages 1985-1998
Published in print June 2009 | ISSN: 0035-8711
Published online May 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14698.x
Resistive relaxation of a magnetically confined mountain on an accreting neutron star

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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 τI∼ 105–108 yr (depending on the conductivity of the neutron star crust) for an accreted mass of Ma= 1.2 × 10−4 M. The magnetic dipole moment simultaneously re-emerges as the screening currents dissipate over τI. For non-axisymmetric 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 τI by 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.

Keywords: accretion, accretion discs; stars: magnetic fields; stars: neutron; pulsars: general

Journal Article.  9235 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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