Modelling the Tidal Disruption Frequency for Neutron Star-Black Hole Binary Systems

Abstract

Gravitational waves (GWs) from neutron star-black hole binary systems (NSBHs) are a promising probe of the neutron star equation of state. One needs to model these waveforms accurately to gain information from NSBH waveform signals. A unique feature of NSBHs is that the merger can happen in a disruptive manner, i.e. the neutron star can get tidally disrupted before it merges with the black hole for a certain parameter subspace of the system. This unique feature has a distinct imprint on the GWs an NSBH produces. Understanding the tidal disruption of the neutron star by a companion black hole plays a vital role in accurately modelling waveforms. We construct an effective action considering dynamical tidal effects and aligned spin interactions in our work. We can use the action to set up an energy balance from which we can compute the orbital frequency at which the neutron star tidally disrupts. The parameter region of validity is given by Λ2 ∈ [1, 5000], Q ∈ [1, 10], χNS and χBH ∈ [−0.5, 0.5]. It is shown that this novel model agrees with numerical relativity (NR) results and significantly outperforms the merger frequencies obtained from the current waveform model PhenomNSBH. Furthermore, recommendations are made for further NR simulations to verify the model such that it can be used to generate accurate gravitational waveforms.