arXiv subjects

T. J. Hutchins

Publications and source records attributed to T. J. Hutchins.

3 recordsLinked to original sources

arXiv2026

Numerical calculations of neutron star mountains supported by crustal lattice pressure

Gravitational waves may set the spin frequencies of neutron stars in low-mass X-ray binaries (LMXBs). One mechanism for facilitating such emission is the formation of a mass asymmetry - or 'mountain' - supported by elastic strains driven by thermal gradients. Most studies have focused either on the origin of the elastic strains or the temperature asymmetry in isolation, and have not considered the entire formation process. In previous work, we showed that anisotropic heat transport in magnetised accreting neutron stars can source a significant temperature asymmetry, and made rough estimates that suggested temperature-induced perturbations in the pressure supplied by the crustal lattice may be competitive with the widely known model of temperature-induced capture-layer shifts. In this paper we carry out detailed calculations to properly explore this scenario. We self-consistently calculate both the temperature asymmetries, the perturbations in crustal lattice pressure, and the mass asymmetries within a single framework. For the first time, we make use of the set of realistic equations of state from the Brussels-Montreal nuclear energy-density functionals BSk19, BSk20, and BSk21 which describe all regions of accreting neutron stars in a thermodynamically consistent, unified way. We find these mountains are too small to be dictating the spin-equilibrium of LMXBs, and estimate the level of gravitational wave emission they produce.

astro-ph.HE↗

arXiv2026

Crustal lattice pressure as a source of neutron star mountains

The spin frequencies of neutron stars in low-mass X-ray binaries may be limited by the emission of gravitational waves. A candidate for producing such steady emission is a mass asymmetry, or "mountain", sourced by temperature asymmetries in the star's crust. A number of studies have examined temperature-induced shifts in the crustal capture layers between one nuclear species and another to produce this asymmetry, with the presence of capture layers in the deep crust being needed to produce the required mass asymmetries. However, modern equation of state calculations cast doubt on the existence of such deep capture layers. Motivated by this, we investigated an alternative source of temperature dependence in the equation of state, coming from the pressure supplied by the solid crustal lattice itself. We show that temperature-induced perturbations in this pressure, while small, may be significant. We therefore advocate for more detailed calculations, self-consistently calculating both the temperature asymmetries, the perturbations in crustal lattice pressure, and the consequent mass asymmetries, to establish if this is a viable mechanism for explaining the observed distribution of low-mass X-ray binary spin frequencies. Furthermore, the crustal lattice pressure mechanism does not require accretion, extending the possibility for such thermoelastic mountains to include both accreting and isolated neutron stars.

astro-ph.HE↗

arXiv2023

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 (LMXB) systems shows a concentration of pulsars well below the Keplarian 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 ($ρ\sim 10^{13}$ 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 $\sim 10^{12}$ G.

astro-ph.HE↗