I-Love-Q relations for a generic family of neutron star equations of state

Abstract

ABSTRACT Neutron stars (and quark stars) have recently been found to follow certain universality, the I-Love-Q relations. These relations can provide a greater understanding of the structural and macro properties of compact astrophysical objects with knowledge of any one of the observable. The reason behind this is the lack of sensitivity to the relations with the equation of state (EoS) of matter. In this work, we have investigated the consistency of universal relations for a generic family of equations of state. These equations of state are consistent with the prescribed limits of nuclear theory (low densities) and perturbative QCD (asymptotically high densities) and respecting recent astronomical observations. At intermediate densities, the equations of states are parametrized by the adiabatic speed of sound. Although the spread in the EoS is significant, the universal nature of the I-Love-Q trio holds relatively well up to a specific tolerance limit of 5 per cent fractional percentage error. We have compared the result first with a similar set, but not respecting the recent astrophysical constraints. A deviation from universality is seen and the tolerance exceeds the 5 per cent limit. Next, we have compared our result with a family of EoS having monotonic sound speed inside a neutron star. A slight deviation from universality is seen for this case; however, the tolerance remains within the 5  per cent limit. This shows the existence of a correlation between universal relations and observational constraints.