http://arxiv.org/abs/1807.11581
Using parametric equations of state (EOS) to model dense-matter phase transitions, we study global, measurable astrophysical parameters of neustron stars (NS), such as their allowed radii and tidal deformabilities, as well as the influence of stiffness of matter before the onset of the phase transitions on the parameters of the possible exotic dense phase. We compare the parameter space of the dense matter EOS permitting phase transitions to a sub-space compatible with by current observational constraints, such as the maximum observable mass, tidal deformabilities of NS-NS mergers, radii of configurations before the onset of the phase transition, and to give predictions for future observations. We study solutions of the TOV equations for a flexible set of parametric EOS, constructed using a realistic description of NS crust, and relativistic polytropes connected by a density-jump phase transition to a simple bag model description of deconfined quark matter. We also compare tidal deformabilities of stars with weak and strong phase transitions with the results of the GW170817 NS-NS merger. Specifically, we study characteristic phase transition features in the $\Lambda_1-\Lambda_2$ relation, and estimate the deviations of our results from the approximate formulae for $\tilde{\Lambda}-R(M_1)$ and $\Lambda$-compactness, proposed in the literature. We find constraints on a hybrid EOS to produce stable NS on the twin branch. For the exemplary EOS most of the high-mass twins can be formed for the minimal values of the density jump $\lambda = 1.33-1.54$ and square of the speed of sound $\alpha = 0.7-0.37$. We compare results with gravitational waves observations and theoretical causal limit and find out that the more favorable EOS have phase transition point at the baryon density around $0.34-0.51$ [fm$^{-3}$]. Minimal radius that can be produced on a twin branch is between 9.5 and 10.5 km.
M. Sieniawska, W. Turczański, M. Bejger, et. al.
Wed, 1 Aug 18
39/65
Comments: 10 pages, 19 figures, submitted to A&A
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