Abstract
We introduce a family of equations of state (EoS) for hybrid neutron star (NS) matter that is obtained by a two-zone parabolic interpolation between a soft hadronic EoS at low densities and a set of stiff quark matter EoS at high densities within a finite region of chemical potentials mu _H< mu < mu _Q. Fixing the hadronic EoS as the APR one and choosing the color-superconducting, nonlocal NJL model with two free parameters for the quark phase, we perform Bayesian analyses with this two-parameter family of hybrid EoS. Using three different sets of observational constraints that include the mass of PSR J0740+6620, the tidal deformability for GW170817, and the mass-radius relation for PSR J0030+0451 from NICER as obligatory (set 1), while set 2 uses the possible upper limit on the maximum mass from GW170817 as an additional constraint and set 3 instead of the possibility that the lighter object in the asymmetric binary merger GW190814 is a neutron star. We confirm that in any case, the quark matter phase has to be color superconducting with the dimensionless diquark coupling approximately fulfilling the Fierz relation eta _D=0.75 and the most probable solutions exhibiting a proportionality between eta _D and eta _V, the coupling of the repulsive vector interaction that is required for a sufficiently large maximum mass. We used the Bayesian analysis to investigate with the method of fictitious measurements the consequences of anticipating different radii for the massive 2~M_odot PSR J0740+6220 for the most likely equation of state. With the actual outcome of the NICER radius measurement on PSR J0740+6220 we could conclude that for the most likely hybrid star EoS would not support a maximum mass as large as 2.5~M_odot so that the event GW190814 was a binary black hole merger.
Highlights
The observation of the first binary neutron star merger GW170817 in gravitational waves [1] and the subsequent electromagnetic signals from the gamma-ray burst to the light curve of the kilonova [2] have opened the era of multimessenger astronomy
The horizontal black dashed lines show the mass range for the lighter object in the binary merger GW190814, that we employ as a possible lower limit on the maximum mass, in the case that this object was a neutron star
We suggest three sets of constraints: 1: the mass measurement for PSR J0740+6620 [55] as the lower limit for the maximum mass, the tidal deformability from GW170817 [4] and the mass-radius constraint from PSR J0030+0451 [58]; 2: in addition to the constraints of set 1, the constraint on the upper limit of the maximum mass from Ref. [60] is included; 3: as for set 1, but assuming that the lower mass companion of the black hole in the asymmetric binary merger GW190814 [3] was a neutron star, the lower limit for the maximum mass is replaced by the lower limit on its mass M190814 = 2.59+−00
Summary
The observation of the first binary neutron star merger GW170817 in gravitational waves [1] and the subsequent electromagnetic signals from the gamma-ray burst to the light curve of the kilonova [2] have opened the era of multimessenger astronomy. In-between these limiting cases, the more realistic scenario of the firstorder phase transition would consider structures of finite size formed by the balance between Coulomb interactions and surface tension (pasta phases), see [10] and references therein This approach has been used recently for a Bayesian analysis with observational constraints for masses and radii of neutron stars [11] which reaches the conclusion that very likely the phase transition onset occurs in the center of neutron stars with masses around 1 M and would match the observed compactness [5] in this way.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
