Ultracompact hybrid stars consistent with multimessenger astrophysics

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.

Automated summary

In this study, we investigate the impact of phase transitions in dense QCD on compact stars and their implications for gravitational wave and x-ray astrophysics observations. Our modeling assumes a strong first-order phase transition after the hadronic branch of compact stars reaches the two-solar mass limit. Our analysis suggests the existence of ultracompact stars with very small radii (6-9 km), which are consistent with the current multimessenger data.