Continuous Gravitational Waves from Thermo-Elastic Mountains in Ultraluminous X-ray Pulsars
Abstract
Fast-spinning, nonaxisymmetrically deformed neutron stars (NSs) are promising targets for continuous gravitational-wave (CGW) searches with current and next-generation ground-based detectors. Ultraluminous X-ray pulsars (ULXPs), characterized by super-Eddington accretion and strong magnetic fields, provide extreme environments in which substantial nonaxisymmetric deformations may develop. In this Letter, we investigate thermo-elastic mountains generated by magnetically induced temperature asymmetries in the accreted crusts of ULXPs. We connect the crustal thermal structure to an accretion-column model and solve the full anisotropic heat-transport equation, extending previous perturbative treatments into the nonlinear, strongly magnetized regime. We find that the weak-field approximation begins to break down near Bref∼1013 G, beyond which nonlinear anisotropic heat transport significantly modifies the quadrupolar thermal response. The resulting thermal asymmetries generate substantial thermo-elastic mass quadrupoles at higher field strengths. Although the currently known ULXPs are unfavorable CGW targets because of their relatively slow spins and, in most cases, large distances, our illustrative spin-evolution calculations show that a NS can enter the super-Eddington accretor phase with a spin period of order 20 ms. Such rapidly rotating Galactic ULXPs could lie within the projected sensitivities of next-generation detectors such as the Einstein Telescope and Cosmic Explorer. These results extend thermal-mountain physics into the strongly magnetized regime relevant to ULXPs and connect super-Eddington accretion with prospective CGW observations.
Related
- Vortex pinning and the elastic response of neutron-star crusts II. Non-axisymmetric loading and Magnus mountains
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- Orientation-dependent sensitivity of the all-sky all-frequency gravitational-wave radiometer search to continuous-wave sources
BibTeX
@misc{li2026continuous,
title = {{Continuous Gravitational Waves from Thermo-Elastic Mountains in Ultraluminous X-ray Pulsars}},
author = {Hong-Bo Li and Ziming Wang and Lijing Shao and Ren-Xin Xu},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.06299},
eprint = {2610.06299},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.06299},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Continuous Gravitational Waves from Thermo-Elastic Mountains in Ultraluminous X-ray Pulsars
AU - Hong-Bo Li
AU - Ziming Wang
AU - Lijing Shao
AU - Ren-Xin Xu
PY - 2026
DA - 2026/10/05
PB - arXiv
DO - 10.48550/arxiv.2610.06299
UR - https://arxiv.org/abs/2610.06299
AB - Fast-spinning, nonaxisymmetrically deformed neutron stars (NSs) are promising targets for continuous gravitational-wave (CGW) searches with current and next-generation ground-based detectors. Ultraluminous X-ray pulsars (ULXPs), characterized by super-Eddington accretion and strong magnetic fields, provide extreme environments in which substantial nonaxisymmetric deformations may develop. In this Letter, we investigate thermo-elastic mountains generated by magnetically induced temperature asymmetries in the accreted crusts of ULXPs. We connect the crustal thermal structure to an accretion-column model and solve the full anisotropic heat-transport equation, extending previous perturbative treatments into the nonlinear, strongly magnetized regime. We find that the weak-field approximation begins to break down near B_ref∼10^13 G, beyond which nonlinear anisotropic heat transport significantly modifies the quadrupolar thermal response. The resulting thermal asymmetries generate substantial thermo-elastic mass quadrupoles at higher field strengths. Although the currently known ULXPs are unfavorable CGW targets because of their relatively slow spins and, in most cases, large distances, our illustrative spin-evolution calculations show that a NS can enter the super-Eddington accretor phase with a spin period of order 20 ms. Such rapidly rotating Galactic ULXPs could lie within the projected sensitivities of next-generation detectors such as the Einstein Telescope and Cosmic Explorer. These results extend thermal-mountain physics into the strongly magnetized regime relevant to ULXPs and connect super-Eddington accretion with prospective CGW observations.
ER -