Relativistic hybrid stars in light of the NICER PSR J0740+6620 radius measurement

Abstract

We explored the implications of the recent radius determination of PSR J0740+6620 by the NICER experiment combined with the neutron skin measurement by PREX-II experiment for the structure of hybrid stars with a strong first-order phase transition from nucleonic to quark matter. We combine a covariant density-functional nucleonic equation of state (EoS) with a constant speed of sound EoS for quark matter. We show that the radius and tidal deformability ranges obtained from GW170817 can be reconciled with the PREX-II results if there is a phase transition to quark matter in the low-mass compact star. In the high-mass segment, the EoS needs to be stiff to comply with the large-radius inference for PSR J0740+6620 and J0030+0451 with a masses M 2M and M 1.4M . We show that twin stars are not excluded, but the mass and radius ranges (with M ≥ M ) are restricted to narrow domains ∆M twin 0.05M and ∆R twin ∼ 1.0 km. We also show that the existence of twin configurations is compatible with the light companion in GW190814 event being a hybrid star in the case of values of the sound-speed square s 0.6.

Universal relations for rapidly rotating cold and hot hybrid star

“…Furthermore, models which describe on the same footing the quark and hadronic phases for astrophysics applications are lacking, therefore a first-order phase transition is often constructed between models of hadronic and quark matter with different underlying theories. A first-order phase transition will affect not only the static properties of compact stars, such as tidal deformabilities measured in gravitational wave events (Paschalidis et al 2018;Montaña et al 2019;Sieniawska et al 2019;Essick et al 2020;Otto et al 2020;Li et al 2020;Jie Li et al 2021;Ferreira et al 2021;Ayriyan et al 2021b), but also their dynamics (Fischer et al 2018;Zha et al 2020;Most et al 2019;Bauswein et al 2019;Prakash et al 2021). Specifically, Fischer et al (2018) and Zha et al (2020) proposed that neutrino and gravitational-wave signals from supernova explosions may contain observable signatures of a phase transition.…”

Probing neutron-star matter in the lab: connecting binary mergers to heavy-ion collisions

“…A meaningful comparison between the regimes probed in BNS mergers and HICs requires a realistic, consistent model for the EOS that is valid across a very large portion of the QCD phase diagram. Such a description should be consistent with constraints from cold compact stars (e.g., [34][35][36][37][38][39][40][41]), properties of symmetric nuclear matter around nuclear saturation density n sat [42][43][44][45][46][47][48][49][50][51][52][53][54][55], as well as large temperature QCD constraints at vanishing and finite density. In the latter case, a consistent description for chiralsymmetry restoration and quark deconfinement must be included to reproduce data from lattice QCD [56][57][58], perturbative QCD [59,60], and high-energy collider experiments [61].…”

Large and massive neutron stars: Implications for the sound speed in dense QCD

“…Given the still large uncertainties involved, the consensus is that current combined data from GW, x-ray, and radio observations are not yet informative enough to identify or rule out microscopic models that exhibit first-order or crossover transitions into exotic matter at densities relevant for neutron stars (for different phase transition scenarios explored, see, e.g., Refs. [55][56][57][58][59][60][61]). We investigated in detail the enhancement in min{c 2 s,max } to reach large R 2.0 when the EOS undergoes a finite discontinuity ∆ε m at low densities, limited by the small tidal deformabilities measured in GW170817.…”