Multimessenger constraints for ultra-dense matter.

Recent rapid progress in multimessenger observations of neutron stars (NSs) offers great potential to constrain the properties of strongly interacting matter under the most extreme conditions. In order to fully exploit the current observational inputs and to study the impact of future observations, we analyze a large ensemble of randomly generated model-independent equations of state (EoSs) and the corresponding rotating stellar structures without the use of quasi-universal relations. We discuss the compatibility and the impact on the EoS of various hypotheses and measurements, including those involving the merger product in GW170817, the binary merger components in GW190814, and radius measurements of PSR J0740+6620. We obtain an upper limit for the dimensionless spin of a rigidly rotating NS, |chi| < 0.84, and find that the conservative hypothesis that the remnant in GW170817 ultimately collapsed to a black hole strongly constrains the EoS and the maximal mass of NSs, implying M_TOV < 2.53M_sol (or M_TOV < 2.19M_sol if we assume that a hypermassive NS was created). Furthermore, we find that radius measurements of massive NSs stars can dramatically limit the EoS, with strict lower limits around 12 km and above offering particularly efficient constraints. Finally, we find that radius values for a two-solar mass NS around 11-13 km would be completely compatible with the presence of quark matter inside massive NSs.