Neutron star mergers

Neutron Star Mergers

Binary neutron star mergers are now believed to be the astrophysical site of the r-process nucleosynthesis. The gravitational-wave event GW170817 is the first direct observation of a neutron star merger. Furthermore, observations of the electromagnetic counterpart enable us to study the properties of the ejecta and it is suggested that the r-process did proceed in GW170817. Simultaneous observations of gravitational waves and electromagnetic signals will be carried out one and another in the future. In order to promote simulation-studies which are necessary to extract physical understanding from there observations, we have developed and optimized a numerical-relativity code that implements general relativity, nuclear equation of state, neutrino radiation transport, and magneto-hydrodynamics in the post-K priority issue 9. We plan to perform a long-term (1 second) simulation of binary neutron star mergers, GW170817, to clarify the dynamics, the mass ejection, and the jet activity in order to compare them with the observations. The simulation results will be used not only for the analysis of GW170817, but also for r-process nucleosynthesis calculations, gravitational-wave observations by gravitational-wave-interferometer such as KAGRA, and electromagnetic-wave observations in the future.