Numerical relativity simulations of compact binaries composed of a black hole and a neutron star

In this master thesis we conducted extensive simulations in the framework of numerical relativity, involving black hole-neutron star binary systems and investigating the parameter space for different mass-ratio’s and spin’s configurations. While existing data predominantly involve binary black holes or binary neutron stars, the analysis of hybrid systems remains incomplete. They represent compelling candidates for the study of ultra-dense matter, offering valuable insights into constraining the equation of state for neutron stars which are today not exactly known. Additionally, they are also expected to produce highly relativistic dynamical ejecta, that can produce heavy elements via rapid neutron capture and whose exact origin is still today a matter of debate. Of particular interest is the potential for kilonovae events, arising from the radioactive decay of the aforementioned heavy nuclei. This subsequent electromagnetic emission positions black hole-neutron star binaries as promising candidates for multimessenger astronomy observations. We started by producing initial data employing the Elliptica code. The data produced in this phase are characterized by irrotational neutron stars, with fixed mass and equation of state. The effects of different massratios and spins are included in the configuration of the black holes, which we simulated with three different values both for mass and spin. The initial data are systematically compared to the effective-one-body model TEOBResumS, and to post-Newtonian models, constructing quasi-equilibrium sequences to analyze tidal and spin-orbit effects that can influence the dynamical evolution. Subsequently, nonspinning initial data are evolved using the BAM code with a specific focus on the finite mass-ratios effects and their impact on the dynamics of the system. An in-depth analysis of the accuracy of the data is then performed, focused on gravitational waveforms, merger remnant, and dynamical ejecta.