EoS in neutron stars – recent results on cooling and tidal deformabilities

The hadronic EoS is obtained from a phenomenological approach that reproduces the properties of nuclear matter and finite nuclei while fulfilling the restrictions on high-density matter deduced from heavy-ion collisions, measurements of massive 2Msun neutron stars, and neutron star radii below 13 km.

On the one hand, we perform cooling simulations and find that the cooling observations are compatible with a soft EoS close to saturation density, hence it generates small neutron star radii. However, our model favors large stellar masses, above 1.8Msun, to explain the colder isolated neutron stars that have been observed, even if nucleon pairing is present. On the other hand, we analyze the possibility of a phase transition leading to twin stars fulfilling the information following the gravitational-wave event GW170817.

We find that the data from GW170817 could be interpreted as produced by the merger of a binary system of hybrid stars, or of a hybrid star with a neutron star. Indeed, our results seem to favor the presence of a hybrid star in the inspiral phase if future gravitational-wave detections measure chirp masses smaller than 1.2Msun and tidal deformabilities of 1.4 Msun less than 400.