Ascertain whether deconfinement phase transitions occur in neutron star cores

Ascertain whether a deconfinement phase transition to quark matter occurs in the cores of neutron stars, and determine the consequences of such a transition for the neutron-star equation of state and associated astrophysical observables.

Background

Beyond hyperonization, the authors note that other proposed changes in the composition of dense matter—such as deconfinement to quark matter—remain observationally unconstrained. Resolving whether deconfinement occurs is essential for understanding the pressure–density relation in neutron star interiors.

This work focuses on neutrino emission via nucleonic direct Urca processes; however, the presence of quark matter would substantially modify cooling pathways and macroscopic properties, making the establishment of deconfinement an open, high-impact question.

References

However, in stark contrast to these observational breakthroughs, the core questions about the internal composition of neutron stars remain unresolved. Although observations clearly confirm the extreme compactness of neutron stars — with radii of $\sim$ 10 km and masses up to 2 $M_{\odot}$ — direct observational constraints on their core composition, such as whether nucleons undergo hyperonization, deconfinement phase transitions, or form meson condensates, are still lacking .

— A Study on the Triggering of Nucleonic Direct Urca Processes in Neutron Stars of Specific Masses and Their Hyperon Dependence  (2509.02988 - Xu et al., 3 Sep 2025) in Section 1 (Introduction), first paragraph