Gravitational wave events involving very massive neutron stars, such as GW190425, have just started to be detected. Although typically classified as binary neutron star mergers, the observed gravitational-wave signal is usually not able to clearly establish a neutron-star nature of the massive primary object in the system. Thus, a black hole--neutron star system cannot be fully ruled out by the gravitational wave detection alone. In the first part of this talk, I will show how early fast ejecta -- only produced in binary neutron star mergers -- can potentially resolve this question and shed light on the nature of the binary system. Focusing on the post-merger evolution of these systems, I will comment on the evolution of magnetic fields and the potential of jet launching from near-equal mass mergers.
In the second part of the talk, we will go beyond the presently observed inspiral phase of a binary neutron star coalescence, and focus on post-merger observables. I will discuss how properties of dense nuclear matter, such as the nuclearsymmetry energy, and out-of-(weak-) equilibrium effects are affecting the post-mergergravitational wave signal. Understanding these various contributions to the post-merger evolution will be key to interpreting next-generation gravitational wave detections.
For additional information, please see https://gravity.princeton.edu/people/elias-most