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, S ₀, and the slope of the symmetry energy, L ₀. We find that the gravitational-wave data are relatively insensitive to S ₀, but that they depend strongly on L ₀ and point to lower values of L ₀ than have previously been reported, with a peak likelihood near L ₀ ∼ 23 MeV. Finally, we use the inferred posteriors on L ₀ to derive new analytic constraints on higher-order nuclear terms.