Updated universal relations for tidal deformabilities of neutron stars from phenomenological equations of state

TL;DR

This paper validates and updates universal relations for neutron star tidal deformabilities using a vast set of phenomenological EOSs, improving their applicability and impact on gravitational wave data analysis.

Contribution

It extends and recalibrates universal relations for neutron star tidal parameters to a broader EOS parameter space, including softer EOSs and larger compactnesses.

Findings

Universal relations are validated and extended to softer EOSs.

Neglecting higher-order tidal effects causes up to 3.5 radians of waveform dephasing.

Updated relations lead to smaller neutron star radius estimates by about 500 meters.

Abstract

Equation of state (EOS) insensitive relations, so-called universal relations, between the neutron star (NS) compactness, its multipolar tidal deformability coefficients, and between the tidal parameters for binary systems are essential to break degeneracies in gravitational wave data analysis. Here, we validate and recalibrate these universal relations using a large set of almost 2 million phenomenological EOSs that are consistent with current observations. In doing so, we extend universal relations to a larger region of the EOS parameter space, most notably to softer EOSs and larger compactnesses. We show that waveform models that neglect higher-than-leading-order tidal deformations of the NSs accumulate as much as $3.5$ radians of dephasing from $20\,{\rm Hz}$ to merger. We also perform a full Bayesian parameter estimation of the GW170817 data, and we compare the NS radius constraints produced using universal relations from the literature and the updated fits we propose here. We find that the new fits yield a NS radius that is smaller by about 500 meters. This difference is less than the statistical uncertainty on the radius at the signal-to-noise-ratio of GW170817, but it is significantly larger than the precision anticipated for next-generation detectors.