Was GW170817 a canonical neutron star merger? Bayesian analysis with a third family of compact stars. (arXiv:2005.02759v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Blaschke_D/0/1/0/all/0/1">David Blaschke</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ayriyan_A/0/1/0/all/0/1">Alexander Ayriyan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Alvarez_Castillo_D/0/1/0/all/0/1">David Alvarez-Castillo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Grigorian_H/0/1/0/all/0/1">Hovik Grigorian</a>
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 $1sigma$ range
that is half of the present value and a larger mass (within the present
$1sigma$ range) would change the posterior likelihood so that a phase
transition onset at $M_{rm onset} = 1.6~M_odot $ would be favored.
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 $1sigma$ range
that is half of the present value and a larger mass (within the present
$1sigma$ range) would change the posterior likelihood so that a phase
transition onset at $M_{rm onset} = 1.6~M_odot $ would be favored.
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