We investigate the possibility that GW170817 was not the merger of two conventional neutron stars ( NS ) , but involved at least one if not two hybrid stars with a quark matter core that might even belong to a third family of compact stars .
To this end , we develop a Bayesian analysis method for selecting the most probable equation of state ( EoS ) under a set of constraints from compact star physics , which now also include the tidal deformability from GW170817 and the first result for the mass and radius determination for PSR J0030+0451 by the NICER Collaboration .
We apply this method for the first time to a two-parameter family of hybrid EoS based on the DD2 model with nucleonic excluded volume for hadronic matter and the color superconducting generalized nlNJL model for quark matter .
The model has a variable onset density for deconfinement and can mimic the effects of pasta phases with the possibility of producing a third family of hybrid stars in the mass-radius diagram .
The main findings of this study are that : ( 1 ) the presence of multiple configurations for a given mass ( twins or even triples ) corresponds to a set of disconnected lines in the \Lambda _ { 1 } - \Lambda _ { 2 } diagram of tidal deformabilities for binary mergers , so that merger events from the same mass range may result in a probability landscape with different peak positions ; ( 2 ) the Bayesian analysis with the above observational constraints favors an early onset of the deconfinement transition , at masses of M _ { onset } \leq 0.8 ~ { } M _ { \odot } with an M - R relationship that in the range of observed neutron star masses is almost indistinguishable from that of a soft hadronic Akmal , Pandharipande , and Ravenhall ( APR ) EoS ; ( 3 ) a few , yet fictitious measurements of the NICER experiment two times more accurate than the present value and a different mass and radius that would change the posterior likelihood so that hybrid EoS with a phase transition onset in the range M _ { onset } = 1.1 - 1.6 ~ { } M _ { \odot } would be favored .