Constraints on high density equation of state from maximum neutron star mass

The low density nuclear matter equation of state is strongly constrained by nuclear properties; however, for constraining the high density equation of state it is necessary to resort to indirect information obtained from the observation of neutron stars, compact objects that may have a central density several times nuclear matter saturation density, n(0). Taking a metamodeling approach to generate a huge set of equations of state that satisfy nuclear matter properties close to n(0) and that do not contain a first-order phase transition, the possibility of constraining the high density equation of state (EOS) was investigated. The entire information obtained from the GW170817 event for the probability distribution of (Lambda) over tilde. was used to make a probabilistic inference of the EOS, which goes beyond the constraints imposed by nuclear matter properties. Nuclear matter properties close to saturation, below 2n(0), do not allow us to distinguish between equations of state that predict different neutron star (NS) maximum masses. This is, however, not true if the equation of state is constrained at low densities by the tidal deformability of the NS merger associated to GW170817. Above 3n(0), differences may be large, for both approaches, and, in particular, the pressure and speed of sound of the sets studied do not overlap, showing that the knowledge of the NS maximum mass may give important information on the high density EOS. Narrowing the maximum mass uncertainty interval will have a sizable effect on constraining the high density EOS.