Measurement of the nuclear symmetry energy parameters from gravitational wave events

The nuclear symmetry energy plays a role in determining both the nuclear properties of terrestrial matter as well as the astrophysical properties of neutron stars. The first measurement of the neutron star tidal deformability, from gravitational wave event GW170817, provides a new way of probing the symmetry energy. In this work, we report on new constraints on the symmetry energy from GW170817. We focus in particular on the low-order coefficients: namely, the value of the symmetry energy at the nuclear saturation density, S₀, and the slope of the symmetry energy, L₀. We find that the gravitational wave data are relatively insensitive to S₀, but that they depend strongly on L₀ and point to lower values of L₀ than have previously been reported, with a peak likelihood near L₀ ∼ 20 MeV. Finally, we use the inferred posteriors on L₀ to derive new analytic constraints on higher-order nuclear terms.