Universal relationships for neutron stars from perturbative approach

TL;DR

This paper investigates universal relationships among neutron star properties using a perturbative approach with various equations of state, revealing that many relations are insensitive to internal structure details, aiding gravitational wave analysis and tests of gravity.

Contribution

It introduces a perturbative method to derive universal relations for neutron star properties across different equations of state, enhancing understanding of their insensitivity to internal details.

Findings

Most neutron star property relations are insensitive to internal structure.

Universal relations can estimate deformability from moment of inertia.

Relations aid gravitational wave analysis and tests of General Relativity.

Abstract

The universal relationships for compact stars have been investigated employing perturbative approach using canonical (APR) and Brussels-Montreal Skyrme (BSk22, BSk24, BSk26) equations of state describing hadronic matter of neutron stars. The neutron star matter has been considered to be $\beta$-equilibrated neutron-proton-electron-muon matter at the core with a rigid crust. The multipole moments of a slowly rotating neutron star characterize its external gravitational field. These variables are dependent on the interior structure of the neutron star described by the equation of state of the neutron star matter. The properties of neutron stars, such as the mass, the radius, the dimensionless moment of inertia, the compactness, the Love number, the dimensionless tidal deformability and the dimensionless quadrupole moment have been calculated and relations among these quantities have been explored. It is found that most of these relations do not depend sensitively on the details of the internal structure of neutron stars. Such universality implies that the measurement of a single quantity appearing in a universal relation would automatically provide information about the others, notwithstanding the fact that those may not be accessible observationally. These can be used to estimate deformability of compact stars through moment of inertia measurements, to quantify spin in binary inspirals by breaking degeneracies in the detection of gravitational waves and test General Relativity in a way that is independent of nuclear structure.