Bayesian inference of dense matter EOS encapsulating a first-order hadron-quark phase transition from observables of canonical neutron stars

Abstract

[Purpose:] We infer the posterior probability distribution functions (PDFs) and correlations of nine parameters characterizing the EOS of dense neutron-rich matter encapsulating a first-order hadron-quark phase transition from the radius data of canonical NSs reported by LIGO/VIRGO, NICER and Chandra Collaborations. We also infer the quark matter (QM) mass fraction and its radius in a 1.4 M${}_{\odot }$ NS and predict their values in more massive NSs. [Method:] Meta-modelings are used to generate both hadronic and QM EOSs in the Markov-Chain Monte Carlo sampling process within the Bayesian statistical framework. An explicitly isospin-dependent parametric EOS for the $npe\mu$ matter in NSs at $\beta$ equilibrium is connected through the Maxwell construction to the QM EOS described by the constant speed of sound (CSS) model of Alford, Han and Prakash. [Results:] (1) The most probable values of the hadron-quark transition density ${\rho }_t/{\rho }_0$ and the relative energy density jump there $\text{De}\text{ep}/{\text{ep}}_t$ are ${\rho }_t/{\rho }_0=1.6_{-0.4}^{+1.2}$ and $\text{De}\text{ep}/{\text{ep}}_t=0.4_{-0.15}^{+0.20}$ at 68\% confidence level, respectively. The corresponding probability distribution of QM fraction in a 1.4 M${}_{\odot }$ NS peaks around 0.9 in a 10 km sphere. Strongly correlated to the PDFs of ${\rho }_t$ and $\text{De}\text{ep}/{\text{ep}}_t$, the PDF of the QM speed of sound squared $\text{cQMsq}/c^2$ peaks at $0.95_{-0.35}^{+0.05}$, and the total probability of being less than 1/3 is very small. (2) The correlations between PDFs of hadronic and QM EOS parameters are very weak. [Conclusions:] The available astrophysical data considered together with all known EOS constraints from theories and terrestrial nuclear experiments prefer the formation of a large volume of QM even in canonical NSs.

Comments: Added Fig.5 and the associated discussions/references regarding effects of the Seidov condition for first-order phase transition. Physical Review C in press