Nuclear physics aspects of the GW170817 neutron star merger event

Abstract The detection of the GW170817 neutron star merger event by the Advanced LIGO and Virgo collaborations has stimulated an intense research activity regarding novel aspects of nuclear physics, which may play an essential role in the understanding of the merger dynamics. Among those, one of the most relevant regards the nuclear-matter equation of state. The analysis of the gravitational wave signal has shown that the upper limit on the average tidal deformability rules out very stiff equations of state, whereas a lower limit can be extracted from the analysis of the kilonova AT2017gfo signal. Those limits translate into an allowed range for the radius R1.5 of a 1.5 solar mass neutron star, 11.8 km ≲ R1.5 ≲ 13.1 km. On the other hand, radii significantly smaller than 12 km have been suggested by X-ray observations. This clash can be solved if the event GW170817/AT2017gfo would originate from the merger of a hadronic star and a star containing quark matter, as in the two-families and in the twin-stars scenarios.