Linear and Nonlinear Tides in Coalescing Binary Neutron Stars

This project is jointly funded by the Gravitational Physics program and the Established Program to Stimulate Competitive Research (EPSCoR). Tidal interactions, which result in the Moon always facing the Earth with the same side, also impact the coalescence of binary neutron stars (BNSs), leaving a noticeable imprint on the gravitational wave (GW) signal of the binary. The discovery of the BNS event GW190817 by LIGO and Virgo has demonstrated the immense scientific potential of studying tides in BNSs. This award will support research into investigating tidal interactions in BNSs based on first-principle theories and their implications for GW observations. It will also facilitate the training of a graduate student in state-of-the-art analytical and computational methods, contributing to the STEM workforce in the United States. In addition to scientific research, outreach activities will be developed to engage women and other underrepresented minorities in STEM fields. To advance analytical models describing tidal interactions, nonlinear hydrodynamical interactions, referred to as nonlinear tides, will be taken into account. This will involve expanding the perturbed fluid motion into eigenmodes and considering the nonlinear couplings among these modes. The evolution of the modes will then be coupled with the GW-driven orbital decay. It has been suggested that incorporating nonlinear tides may enhance the agreement between analytical models and numerical relativity simulations based on tidal calculations at the Newtonian order. The calculations will be extended to post-Newtonian orders, resulting in readily applicable templates for GW data analysis and comparison with numerical relativity. Additionally, the incorporation of neutron star spins and binary eccentricities will be further explored. Certain computational tools developed during this project will be made publicly accessible online, fostering collaboration and facilitating scientific advancements. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.