The project has developed, for the first time, a set of theoretical models for the complete gravitational spectrum of BNSMs. These waveforms are valid from arbitrarily low (inspiral) frequencies to the kiloHertz emission of the remnants and for any possible binary. The research work focused on the effective-one-body (EOB) framework, an analytical approach to the two-body problem in General Relativity, and on nonlinear simulations in numerical relativity. These methods have been developed in various directions and synergetically combined in order to obtain a unified and complete description of the BNSMs. Computationally efficient yet accurate wave-generation algorithms were developed using either analytical, notably developing the first frequency-domain EOB, phenomenological or machine learning approaches. Several key results have been made publicly available in form of open-source codes and data. They have been applied to the analysis of GW170817, in particular for the measurement of tidal polarizability parameters that is critical to constrain the neutron star's EOS.
BinGraSp performed the largest-to-date simulation campaign to quantitatively investigate the role of binary parameters (masses, spins, mass ratio, and EOS) on the merger dynamics and remnants. Numerical simulations were used to verify the EOB model in the high-frequency merger regime and to further inform EOB by means of flexibility parameters. Simulations have also systematically explored prompt black hole formation and the postmerger phase up to viscous timescales, with an emphasis on the nuclear EOS effects and microphysics (weak interactions). Simulations were the essential basis for developing postmerger GW models to complete the EOB in the kiloHertz regime. Here the main approach developed by the team was to investigate and design quasiuniversal relations connecting spectral features to the binary parameters. These relations are the key theoretical input to constrain the EOS from BNSM observations, and are now widely used in GW astronomy. BinGraSp also developed dedicated Bayesian approaches for the analysis of kiloHertz GWs. Science prospects studies for next generation observatories included the detectability of kiloHertz signals, waveform systematics and constraints on the neutron star's mass-radius diagram.
BinGraSp's simulations proved the necessity and feasibility of comprehensive and systematic computations in General Relativity for the interpretation of astrophysical events. They established a new paradigm in the understanding of BNSMs remnants, which is summarized in two invited reviews on the topic. After GW170817, BinGraSp's research performed one of the first joint GW-kilonova analyses and established a Bayesian framework to coherently analyse multimessenger observations. A highlight from this research is the first application of Bayesian model selection to the kilonova data aimed at ranking different hypothesis on the ejecta morphology. The open-access ejecta data were also employed in the first ab-initio calculation of kiklnova spectra combining simulations, nuclear networks and radiation transport calculations.
