Hybrid Quark Stars with Quark-Quark Phase Transitions

TL;DR

This paper investigates the existence and properties of hybrid quark stars with quark-quark phase transitions, analyzing their mass-radius relations, observational constraints, and potential for twin star configurations.

Contribution

It introduces models of hybrid quark stars with sharp quark-quark phase transitions and explores their observational signatures and constraints, expanding the understanding of possible compact star types.

Findings

Identification of viable parameter space consistent with recent observations.

Discovery of twin star configurations in hybrid quark star models.

Deviation from universal relations in postmerger frequencies due to quark-quark phase transitions.

Abstract

We explore the possibility of phase transitions between different quark matter phases occurring within quark stars, giving rise to the hybrid quark stars (HybQSs). First, we obtain the generic phase diagram of possible mass-radius relation forms for the HybQSs. Then, utilizing a well-established general parameterization of interacting quark matter, we construct quark star models featuring sharp first-order quark-quark phase transitions of various types, in contrast to the hadron-quark transition in conventional hybrid stars. We systematically investigate how recent observations, such as the pulsar mass measurement $M_{\rm TOV}\gtrsim2M_{\odot}$ and the GW170817's tidal deformability bound $\Lambda_{1.4M_{\odot}}<800$, constrain the viable parameter space. We also identified twin stars in some of the HybQS parameter space. Furthermore, we found that the quark-quark phase transitions in hybrid quark stars may also cause the deviation from the approximate universal relation between the dominant postmerger frequency $f_{\rm peak}$ and tidal deformability $\Lambda_{1.35M_{\odot}}$, which was previously believed to only be caused by the hadron-quark phase transitions in hybrid neutron stars. This work unveils new possibilities of phase transitions and the resulting new types of compact stars in realistic astrophysical scenarios.