Neutron star mergers: Fast ejecta, magnetic fields and dense matter

Elias Most (Princeton/IAS)

November 01, 2021

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Abstract: 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 nuclear symmetry energy, and out-of-(weak-) equilibrium effects are affecting the post-merger gravitational wave signal. Understanding these various contributions to the post-merger evolution will be key to interpreting next-generation gravitational wave detections.