Gravitational radiation from thermal mountains on accreting neutron stars: sources of temperature non-axisymmetry
Gravitational radiation from thermal mountains on accreting neutron stars: sources of temperature non-axisymmetry
The spin distribution of accreting neutron stars in low-mass X-ray binary systems shows a concentration of pulsars well below the Keplerian break-up limit. It has been suggested that their spin frequencies may be limited by the emission of gravitational waves, due to the presence of large-scale asymmetries in the internal temperature profile of the star. These temperature asymmetries have been demonstrated to lead to a non-axisymmetric mass distribution, or ‘mountain’, that generates gravitational waves at twice the spin frequency. The presence of a toroidal magnetic field in the interior of accreting neutron stars has been shown to introduce such anisotropies in the star’s thermal conductivity, by restricting the flow of heat orthogonal to the magnetic field and establishing a non-axisymmetric temperature distribution within the star. We revisit this mechanism, extending the computational domain from (only) the crust to the entire star, incorporating more realistic microphysics, and exploring different choices of outer boundary condition. By allowing a magnetic field to permeate the core of the neutron star, we find that the likely level of temperature asymmetry in the inner crust (ρ ∼ 10
13 g cm
−3) can be up to 3 orders of magnitude greater than the previous estimate, improving prospects for one day detecting continuous gravitational radiation. We also show that temperature asymmetries sufficiently large to be interesting for gravitational wave emission can be generated in strongly accreting neutron stars if crustal magnetic fields can reach ∼10
12 G.
accretion, accretion discs, gravitational waves, magnetic fields, stars: neutron
226-251
Hutchins, Thomas James
4873dc98-1d21-4512-b498-2a79a9bdfe14
Jones, David
b8f3e32c-d537-445a-a1e4-7436f472e160
31 March 2023
Hutchins, Thomas James
4873dc98-1d21-4512-b498-2a79a9bdfe14
Jones, David
b8f3e32c-d537-445a-a1e4-7436f472e160
Hutchins, Thomas James and Jones, David
(2023)
Gravitational radiation from thermal mountains on accreting neutron stars: sources of temperature non-axisymmetry.
Monthly Notices of the Royal Astronomical Society, 522 (1), .
(doi:10.1093/mnras/stad967).
Abstract
The spin distribution of accreting neutron stars in low-mass X-ray binary systems shows a concentration of pulsars well below the Keplerian break-up limit. It has been suggested that their spin frequencies may be limited by the emission of gravitational waves, due to the presence of large-scale asymmetries in the internal temperature profile of the star. These temperature asymmetries have been demonstrated to lead to a non-axisymmetric mass distribution, or ‘mountain’, that generates gravitational waves at twice the spin frequency. The presence of a toroidal magnetic field in the interior of accreting neutron stars has been shown to introduce such anisotropies in the star’s thermal conductivity, by restricting the flow of heat orthogonal to the magnetic field and establishing a non-axisymmetric temperature distribution within the star. We revisit this mechanism, extending the computational domain from (only) the crust to the entire star, incorporating more realistic microphysics, and exploring different choices of outer boundary condition. By allowing a magnetic field to permeate the core of the neutron star, we find that the likely level of temperature asymmetry in the inner crust (ρ ∼ 10
13 g cm
−3) can be up to 3 orders of magnitude greater than the previous estimate, improving prospects for one day detecting continuous gravitational radiation. We also show that temperature asymmetries sufficiently large to be interesting for gravitational wave emission can be generated in strongly accreting neutron stars if crustal magnetic fields can reach ∼10
12 G.
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2212.07452
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stad967
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Accepted/In Press date: 28 March 2023
e-pub ahead of print date: 31 March 2023
Published date: 31 March 2023
Additional Information:
Funding Information:
We wish to thank Anthea Fantina and Nicolas Chamel for sharing data on the pressure-density relations for the BSk19-21 EoSs, as well as Ian Hawke for providing assistance with the construction of our numerical code. We also thank Nils Andersson and Andreas Schmitt for helpful conversations relating to magnetic fields in the presence of proton superconductivity. Additionally we acknowledge useful discussion with Ed Brown and Wynn Ho regarding various aspects of our thermal model. TH acknowledges support from the Science and Technology Facilities Council (STFC) through Grant No. ST/T5064121/1. DIJ also acknowledges support from the STFC via grant No. ST/R00045X/1.
Publisher Copyright:
© 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
Keywords:
accretion, accretion discs, gravitational waves, magnetic fields, stars: neutron
Identifiers
Local EPrints ID: 476658
URI: http://eprints.soton.ac.uk/id/eprint/476658
ISSN: 1365-2966
PURE UUID: 9e58630f-2730-4596-acc4-fe953a251847
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Date deposited: 10 May 2023 17:18
Last modified: 17 Mar 2024 02:48
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Thomas James Hutchins
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