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Gravitational waves from magnetically-induced thermal neutron star mountains

Gravitational waves from magnetically-induced thermal neutron star mountains
Gravitational waves from magnetically-induced thermal neutron star mountains
Many low-mass X-ray binary (LMXB) systems are observed to contain rapidly spinning neutron stars. The spin frequencies of these systems may be limited by the emission of gravitational waves. This can happen if their mass distribution is sufficiently non-axisymmetric. It has been suggested that such `mountains' may be created via temperature non-axisymmetries, but estimates of the likely level of temperature asymmetry have been lacking. To remedy this, we examine a simple symmetry breaking mechanism, where an internal magnetic field perturbs the thermal conductivity tensor, making it direction-dependent. We find that the internal magnetic field strengths required to build mountains of the necessary size are very large, several orders of magnitude larger than the inferred external field strengths, pushing into the regime where our assumption of the magnetic field having a perturbative effect on the thermal conductivity breaks down. We also examine how non-axisymmetric surface temperature profiles, as might be caused by magnetic funnelling of the accretion flow, lead to internal temperature asymmetries, but find that for realistic parameters the induced non-axisymmetries are very small. We conclude that, in the context of this work at least, very large internal magnetic fields are required to generate mountains of the necessary size.
astro-ph.HE, gr-qc
0035-8711
2839–2850
Osborne, E. L.
189d5fa4-4488-4e6c-a9d3-75bdb9e9c666
Jones, D. I.
b8f3e32c-d537-445a-a1e4-7436f472e160
Osborne, E. L.
189d5fa4-4488-4e6c-a9d3-75bdb9e9c666
Jones, D. I.
b8f3e32c-d537-445a-a1e4-7436f472e160

Osborne, E. L. and Jones, D. I. (2020) Gravitational waves from magnetically-induced thermal neutron star mountains. Monthly Notices of the Royal Astronomical Society, 494 (2), 2839–2850. (doi:10.1093/mnras/staa858).

Record type: Article

Abstract

Many low-mass X-ray binary (LMXB) systems are observed to contain rapidly spinning neutron stars. The spin frequencies of these systems may be limited by the emission of gravitational waves. This can happen if their mass distribution is sufficiently non-axisymmetric. It has been suggested that such `mountains' may be created via temperature non-axisymmetries, but estimates of the likely level of temperature asymmetry have been lacking. To remedy this, we examine a simple symmetry breaking mechanism, where an internal magnetic field perturbs the thermal conductivity tensor, making it direction-dependent. We find that the internal magnetic field strengths required to build mountains of the necessary size are very large, several orders of magnitude larger than the inferred external field strengths, pushing into the regime where our assumption of the magnetic field having a perturbative effect on the thermal conductivity breaks down. We also examine how non-axisymmetric surface temperature profiles, as might be caused by magnetic funnelling of the accretion flow, lead to internal temperature asymmetries, but find that for realistic parameters the induced non-axisymmetries are very small. We conclude that, in the context of this work at least, very large internal magnetic fields are required to generate mountains of the necessary size.

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More information

Accepted/In Press date: 24 April 2020
Published date: 29 April 2020
Additional Information: Updated to match version to appear in MNRAS
Keywords: astro-ph.HE, gr-qc

Identifiers

Local EPrints ID: 439617
URI: http://eprints.soton.ac.uk/id/eprint/439617
ISSN: 0035-8711
PURE UUID: 59858fa8-73e4-4b61-9c85-bce1e898df34
ORCID for D. I. Jones: ORCID iD orcid.org/0000-0002-0117-7567

Catalogue record

Date deposited: 28 Apr 2020 16:30
Last modified: 07 Oct 2020 01:43

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Contributors

Author: E. L. Osborne
Author: D. I. Jones ORCID iD

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