http://arxiv.org/abs/2005.02759
We investigate the possibility that GW170817 has not been the merger of two conventional neutron stars (NS) but that at least one of them was a hybrid star with a quark matter core, possibly belonging to a third family of compact stars. We present a Bayesian analysis method for selecting the most probable equation of state (EoS) under a set of constraints, which include besides the maximum mass also the tidal deformability from GW170817 and the first mass and radius measurement by the NICER Collaboration for PSR J0030+0451. 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 effects of pasta phases with the possibility of producing a third family of hybrid stars in the mass-radius ($M-R$) diagram. The main findings of this study are that: 1) the presence of multiple configurations for a given mass 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 $M_{\rm onset}\approx 0.5~M_\odot$ with a $M-R$ relationship that in the range of observed neutron star masses is almost indistinguishable from that of a soft hadronic APR EoS; 3) a yet fictitious measurement of the NICER experiment with a $1\sigma$ range that is half of the present value and a larger mass (within the present $1\sigma$ range) would change the posterior likelihood so that a phase transition onset at $M_{\rm onset} = 1.6~M_\odot $ would be favored.
D. Blaschke, A. Ayriyan, D. Alvarez-Castillo, et. al.
Thu, 7 May 20
33/62
Comments: 20 pages, 18 figures
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