Relativistic Hybrid Stars with Sequential First-order Phase Transitions in Light of Multimessenger Constraints

In this work, we consider the properties of compact stars in which quark matter has low- and high-density phases that are separated by a first-order phase transition. Thus, unlike the commonly considered case of a single phase transition from hadronic to quark matter, our models of hybrid stars contain sequential phase transitions from hadronic matter to low- and then to high-density quark matter phases. We extend our previous study of the parameter space of hybrid stars with a single phase transition to those with sequential phase transitions, taking into account the constraints on the mass and radius of neutron stars from the NICER experiment, the experimental inferences of the neutron skin thickness of the lead nucleus by the PREX-II experiment, and constraints on the tidal deformability from the gravitational-wave event GW170817. We determine the range of the masses for which both twin and triplet configurations, i.e., identical-mass stars with two and three different values of radii, arise.

Automated summary

In this work, we investigate the properties of compact stars with a first-order phase transition, where quark matter has low- and high-density phases. Unlike the usual case of a single phase transition, our hybrid star models involve sequential phase transitions from hadronic matter to low-density quark matter, and then to high-density quark matter phases. We explore the parameter space of these hybrid stars, considering constraints from neutron star mass, radius measurements, neutron skin thickness observations, and tidal deformability constraints from a gravitational-wave event.