Gravitational-wave Emission from a Primordial Black Hole Inspiraling inside a Compact Star: A Novel Probe for Dense Matter Equation of State

Primordial black holes of planetary masses captured by compact stars are widely studied to constrain their composition fraction of dark matter. Such a capture may lead to an inspiral process and be detected through gravitational-wave signals. In this Letter, we study the postcapture inspiral process by considering two different kinds of compact stars, i.e., strange stars and neutron stars. The dynamical equations are numerically solved, and the gravitational-wave emission is calculated. It is found that the Advanced LIGO can detect the inspiraling of a 10−5 M⊙ primordial black hole at a distance of 10 kpc, while a Jovian-mass case can even be detected at megaparsecs. Promisingly, the next generation of gravitational-wave detectors can detect cases of 10−5 M⊙ primordial black holes up to ∼1Mpc and Jovian-mass cases at several hundred megaparsecs. Moreover, the kilohertz gravitational-wave signal shows significant differences for strange stars and neutron stars, potentially making it a novel probe to the dense matter equation of state.