Dynamics of Mixed Binary Mergers using Numerical Relativity Simulations
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Neutron star black hole (NSBH) mergers have captured the interest of physicists for more than 50 years. The study of these objects can provide valuable insights to understand the origins of heavy elements in the universe, the cause of short gamma ray burst, the equation of state of neutron stars, and the quantum nature of gravity. However, they still remain the most elusive binary with no confirmed gravitational or electromagnetic detections till date. One of the primary challenges to identify NSBH sources is high similarity in the gravitational waves signatures of this system with binary black holes and double neutron stars. Hence, we require the tools of numerical relativity to design accurate templates of gravitational waves and identify key features to differentiate between the signals of NSBH systems from other binaries. In this work, we perform relativistic hydrodynamical simulations of non-spinning neutron star black hole mergers using a new initial data method. Through an extensive comparison, we show the efficiency of our models with published works by analyzing the orbital dynamics, remnant properties and gravitational wave signatures. We also investigate the differences between the coalescence of binary black hole and mixed binary system as a function of initial conditions. Our results indicate that due to strong tidal disruption, low mass ratio and low compactness systems have the strongest deviation from corresponding vacuum binary. Early disruption in these cases lead to the formation of accretion disk and dynamical ejecta which impacts the post merger gravitational wave signal. Higher mass ratio or higher compactness system, on the other hand, barely faces any disruption leading to gravitational wave signals similar to a binary black hole. In such scenarios, any differences if exist, are found to be most prominent in higher-order modes. Thus, in addition to model accuracy, the orientation of the signal would also play an important role in mixed binary detections.