Constraining the nuclear equation of state from orbits of primordial black holes inside neutron stars

TL;DR

This paper proposes that gravitational wave observations of primordial black holes orbiting inside neutron stars can provide new constraints on the nuclear equation of state, complementing existing astrophysical measurements.

Contribution

It introduces a novel method to constrain the nuclear EOS by analyzing gravitational wave signals from black holes orbiting within neutron stars.

Findings

Orbital precession causes detectable beat phenomena in gravitational waves.

Different EOSs produce distinct orbital and gravitational wave signatures.

Observing these signals can break degeneracies in current EOS constraints.

Abstract

Lacking terrestrial experimental data, our best constraints on the behavior of matter at high densities up to and above nuclear density arise from observations of neutron stars. Current constraints include those based on measurements of stellar masses, radii, and tidal deformabilities. Here we explore how orbits of primordial black holes - should they exist - inside neutron stars could provide complementary constraints on the nuclear equation of state (EOS). Specifically, we consider a sample of candidate EOSs, construct neutron star models for these EOSs, and compute orbits of primordial black holes inside these stars. We discuss how the pericenter advance of eccentric orbits, i.e. orbital precession, results in beat phenomena in the emitted gravitational wave signal. Observing this beat frequency could constrain the nuclear EOS and break possible degeneracies arising from other constraints, as well as provide information about the host star.