Astrophysics from a Neutron Star Merger

Coordinators: Duncan Brown, Daniel Kasen, and Ehud Nakar

The observation of the binary neutron star merger GW170817 by LIGO, Virgo, Fermi, and Integral has led to a plethora of new astrophysical insights. The gravitational-wave signal enabled the measurement of the mass of the neutron stars and the first exploration of the equation of state of matter at super-nuclear densities. The association of the gamma-ray and gravitational-wave signals confirmed the long-held hypothesis that the mergers of neutron stars are the progenitors of one class of gamma-ray bursts. LIGO/Virgo’s localization on the sky enabled the rapid identification of an optical counterpart in the outskirts of the NGC 4993 at the remarkably close distance of 40 Mpc.

The subsequent electromagnetic observations yielded a number of firsts, including the detection and characterization of a kilonova and direct confirmation that r-process nucleosynthesis was active in the emitted ejecta. However, may open questions remain. What was the fate of the merger remnant? Was the ejecta dynamical (from the time of the merger) or did it came later from a slower wind from merger-remnant disk? Given how close the source was, why was the gamma-ray burst so faint? Is there a late-time emergence of a jet from the disk/merger remnant interaction? This rapid-response workshop will bring together a broad range of experts to discuss the astrophysics that can be learned from the observations of GW170817. 

There will be an associated four day conference on Dec 5, 6, 7 and 8, 2017 entitled: "Understanding GW170817: The First Double Neutron Star Merger" that will highlight the observational status as well as the open theoretical puzzles.