Implications from GW170817 and I-Love-Q relations for relativistic hybrid stars

TL;DR

This paper develops new models for hybrid hadron-quark stars, tests their consistency with GW170817, and finds that I-Love-Q relations are similar across different star types, enabling better tests of gravity.

Contribution

It introduces new parametrizations for hybrid star equations of state and demonstrates their compatibility with gravitational wave data and universal relations.

Findings

GW170817 is consistent with a binary hybrid star-neutron star merger.

I-Love-Q relations for hybrid stars are within 3% of those for hadronic and quark stars.

Universal relations can aid in testing gravity and distinguishing star types in gravitational wave observations.

Abstract

Gravitational wave observations of GW170817 placed bounds on the tidal deformabilities of compact stars allowing one to probe equations of state for matter at supranuclear densities. Here we design new parametrizations for hybrid hadron-quark equations of state, that give rise to low-mass twin stars, and test them against GW170817. We find that GW170817 is consistent with the coalescence of a binary hybrid star--neutron star. We also test and find that the I-Love-Q relations for hybrid stars in the third family agree with those for purely hadronic and quark stars within $\sim 3\%$ for both slowly and rapidly rotating configurations, implying that these relations can be used to perform equation-of-state independent tests of general relativity and to break degeneracies in gravitational waveforms for hybrid stars in the third family as well.