Constraining properties of high-density matter in neutron stars with magneto-elastic oscillations

TL;DR

This paper uses magneto-elastic oscillation models and Bayesian analysis of magnetar QPOs to constrain neutron star properties, including magnetic field strength, crust thickness, and internal composition, advancing understanding of high-density matter.

Contribution

It introduces a Bayesian framework linking magnetar oscillation data to neutron star interior properties, providing new constraints on magnetic fields, crust thickness, and core superfluidity.

Findings

Estimated magnetic field strength $ar B o 2.1^{+1.3}_{-1.0} imes10^{15} ext{ G}$

Crust thickness $ o 1.6^{+0.7}_{-0.6} ext{ km}$

Favors presence of superfluid phase and low stellar compactness

Abstract

We discuss torsional oscillations of highly magnetised neutron stars (magnetars) using two-dimensional, magneto-elastic-hydrodynamical simulations. Our model is able to explain both the low- and high-frequency quasi-periodic oscillations (QPOs) observed in magnetars. The analysis of these oscillations provides constraints on the breakout magnetic-field strength, on the fundamental QPO frequency, and on the frequency of a particularly excited overtone. More importantly, we show how to use this information to generically constraint properties of high-density matter in neutron stars, employing Bayesian analysis. In spite of current uncertainties and computational approximations, our model-dependent Bayesian posterior estimates for SGR 1806-20 yield a magnetic-field strength $\bar B\sim 2.1^{+1.3}_{-1.0}\times10^{15}\,$G and a crust thickness of $\Delta r = 1.6^{+0.7}_{-0.6}$ km, which are both in remarkable agreement with observational and theoretical expectations, respectively (1-$\sigma$ error bars are indicated). Our posteriors also favour the presence of a superfluid phase in the core, a relatively low stellar compactness, $M/R<0.19$, indicating a relatively stiff equation of state and/or low mass neutron star, and high shear speeds at the base of the crust, $c_s>1.4\times10^8\,$cm/s. Although the procedure laid out here still has large uncertainties, these constraints could become tighter when additional observations become available.