Ultracompact hybrid stars consistent with multimessenger astrophysics

TL;DR

This paper models ultracompact hybrid stars with a strong first-order QCD phase transition, predicting very small radii consistent with current multimessenger astrophysics data, including gravitational waves and X-ray observations.

Contribution

It introduces a model of compact stars with a strong first-order phase transition in dense QCD, predicting ultracompact stars with radii of 6-9 km that align with multimessenger observations.

Findings

Ultracompact stars with 6-9 km radii are consistent with current data.

Two-solar mass hadronic stars align with NICER and gravitational wave observations.

Models with a strong QCD phase transition can explain diverse neutron star observations.

Abstract

In this work, we consider the consequences of phase transition in dense QCD on the properties of compact stars and implications for the observational program in gravitational wave and X-ray astrophysics. The key underlying assumption of our modeling is a strong first-order phase transition past the point where the hadronic branch of compact stars reaches the two-solar mass limit. Our analysis predicts ultracompact stars with very small radii - in the range of 6-9 km - living on compact star sequences that are entirely consistent with the current multimessenger data. We show that sequences featuring two-solar mass hadronic stars consistent with radio-pulsar observations are also consistent with the inferences of large radii for massive neutron stars by NICER X-ray observations of neutron stars and the small radii predicted by gravitational waves analysis of the binary neutron star inspiral event GW170817 for our models that feature a strong first-order QCD phase transition.