Establish whether meson condensates form in neutron star cores

Establish whether meson condensates form in the cores of neutron stars at high densities, and characterize their impact on the neutron-star equation of state, particle composition, and neutrino cooling behavior.

Background

The formation of meson condensates (e.g., pion or kaon condensates) has been proposed as a mechanism altering the microphysics of dense matter in neutron star cores. The authors highlight the lack of direct observational constraints on such phenomena.

Determining the existence and properties of meson condensates would have significant implications for neutrino emissivity and luminosity from direct Urca processes, potentially offering observational signatures to probe the composition of neutron star interiors.

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