Neutron Star--Primordial Black Hole Binaries: Dynamical Tides, Resonance Locking, and Gravitational Waves

Abstract

The orbital evolution of a neutron star and a much lower-mass primordial black hole can differ strikingly from that of typical compact binaries. Dynamical tides, analogous to those in the Solar System's giant planet-moon systems, can accelerate inspiral or induce outspiral, depending on the orbital configuration. We show how gravitational-wave emission mediates this evolution when neutron star modes remain locked in resonance with the orbit. These effects may leave observable signatures in pulsar timing or gravitational waves.