Effects of neutron-star dynamic tides on gravitational waveforms within the effective-one-body approach (1602.00599v3)

Abstract: Extracting the unique information on ultradense nuclear matter from the gravitational waves emitted by merging, neutron-star binaries requires robust theoretical models of the signal. We develop a novel effective-one-body waveform model that includes, for the first time, dynamic (instead of only adiabatic) tides of the neutron star, as well as the merger signal for neutron-star--black-hole binaries. We demonstrate the importance of the dynamic tides by comparing our model against new numerical-relativity simulations of nonspinning neutron-star--black-hole binaries spanning more than 24 gravitational-wave cycles, and to other existing numerical simulations for double neutron-star systems. Furthermore, we derive an effective description that makes explicit the dependence of matter effects on two key parameters: tidal deformability and fundamental oscillation frequency.

Effects of Neutron-Star Dynamic Tides on Gravitational Waveforms

The paper "Effects of Neutron-Star Dynamic Tides on Gravitational Waveforms within the effective-one-body approach" represents a significant advancement in the modeling of neutron star (NS) dynamics in binary systems, specifically neutron-star–black-hole (NS-BH) and double neutron-star (NS-NS) binaries. The authors introduce a novel effective-one-body (EOB) waveform model which, for the first time, incorporates dynamic tides. This enhancement allows for the detailed analysis of ultradense nuclear matter effects, providing a more accurate description of gravitational-wave signals emitted during NS mergers.

Key Developments and Results

1. Dynamic vs. Adiabatic Tides: The paper emphasizes the importance of including dynamic tides (DT) in the EOB model, opposed to merely adiabatic tides (AT). Dynamic tides arise from tidal forcing frequencies approaching the NS's eigenfrequencies, enhancing the tidal response beyond the static equilibrium modeled by ATs. This is critical for accurately capturing the effects on gravitational waveforms, especially for low mass ratios and NS-BH configurations with substantial NS tidal disruption potential.
2. TEOB Model Construction: The TEOB framework combines post-Newtonian (PN) approximations and strong-field effects in a Hamiltonian form, incorporating the tidal interactions beyond the static adiabatic limit. The DT effects are embedded in the Hamiltonian dynamics via specific resummation techniques and detailed interaction terms, with analysis showing their considerable influence over 24 gravitational-wave cycles.
3. Numerical Relativity (NR) Simulation Comparison: Utilizing high-resolution NR simulations, the authors demonstrate that introducing DT effects in the TEOB model results in substantial improvements in waveform accuracy. This held true for mass ratios $q \leq 3$, where DTs contributed significantly to the late inspiral phase accuracy compared to previously existing models relying on ad hoc amplification of tidal effects.
4. Effective Description of Dynamic Tides: The paper goes further to speculate on practical implementations, introducing an effective description of DT impacts via enhanced tidal deformability parameters. This effective representation aims to bridge the gap between comprehensive dynamic tidal modeling and computational efficiency necessary for real-world gravitational wave analysis.

Implications and Future Directions

The introduction of DTs in the EOB model presents important advancements in theoretical astrophysics and gravitational wave research. It provides a robust tool for the extraction of neutron star equation of state (EoS) parameters from observational data, thus offering a deeper understanding of the nature of ultradense matter. Predictably, DT effects may offer a unique perspective into low mass ratio binary systems, potentially observable by detectors like LIGO and Virgo.

The results advocate for the further exploration of dynamic tidal effects in NS binaries, including the influence of spin interactions and other strong-field phenomena. Additionally, there is scope in refining the EOB model to incorporate comprehensive NR data sets, improving the synchronization between numerical simulations and analytical models.

Overall, the paper contributes significantly to the precision modeling required for gravitational wave astronomy, setting the stage for future studies in NS behavior across diverse astrophysical settings. The effective dynamic-tidal EOB framework not only enhances our capabilities in waveform modeling but also enriches our understanding of the fundamental physics governing NS matter under extreme conditions.