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

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 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.

Automated summary

In this study, universal relations are validated and recalibrated using a large set of phenomenological EOSs, expanding to softer EOSs and larger compactnesses. Neglecting higher-than-leading-order tidal deformations of NSs can result in up to 3.5 radians of dephasing in waveform models from 20 Hz to merger. The new fits yield a NS radius smaller by about 500 meters compared to literature results, highlighting the importance of updated fits for future gravitational wave data analysis.