Editorial: Strong and Weak Interactions in Compact Stars

Mark Alford¹David Blaschke²Ignazio Bombaci³James Lattimer⁴Armen Sedrakian^2,5*

• ¹Department of Physics, Washington University, St.~Louis, Missouri 63130, USA, St. Louis, United States
• ²Institute of Theoretical Physics, Faculty of Physics and Astronomy, University of Wrocław, Wroclaw, Poland
• ³Universita degli Studi di Pisa Dipartimento di Fisica, Pisa, Italy
• ⁴Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 USA, Stony Brook, United States
• ⁵Frankfurt Institute for Advanced Studies, Frankfurt, Germany

The Research Topic "Strong and Weak Interactions in Compact Stars" provides a broad overview of recent advances in the study of the physics of compact stars. The contributions span nuclear and quark matter equations of state, weak interaction rates in dense matter, nucleosynthesis, rotational and thermal effects in neutron stars, and the interpretation of observational constraints. Combined they shed light on the progress achieved and the challenges that remain in constructing a coherent, multi-scale description of compact stars.Several articles focus on the equation of state (EoS) of dense matter, which remains a central uncertainty in neutron star physics. Tong et al. provide a concise review of relativistic Brueckner-Hartree-Fock theory formulated in full Dirac space, emphasizing recent technical advances beyond common angleaveraging approximations and their implications for neutron star structure. Reinforcing this microscopic perspective, Sammaruca and Ajagbonna argue for the use of state-of-the-art ab initio nuclear and neutron matter calculations as a robust baseline for high-density extrapolations. By combining these with causality, maximum-mass constraints, and speed-of-sound-guided parametrizations, they delineate allowed regions of the EoS and present associated predictions for neutron star cooling.The connection between nuclear experiments, astrophysical observations, and dense-matter theory is explored further by Burgio et al., who investigate correlations between the density dependence of the symmetry energy and neutron skin thickness measurements in finite nuclei, in light of recent CREX and PREX results. By analyzing a broad ensemble of microscopic and phenomenological EoS models consistent with neutron star mass and tidal deformability constraints, this work highlights emerging tensions between laboratory data and current theoretical descriptions of the nuclear EoS.Strong interactions at even higher densities, where deconfined quark matter may appear, are addressed in several contributions. Alford et al. study the bulk viscosity of warm, dense, neutrino-transparent quark matter in the two-flavor color-superconducting (2SC) phase driven by weak interaction β-decays (Urca reactions). Using an extended SU(3) Nambu-Jona-Lasinio model, they demonstrate a pronounced sensitivity of bulk viscosity and damping timescales to vector interactions, with important implications for the dissipation of density oscillations in merging compact stars. In a complementary phenomenological approach, Kourmpetis et al. explore whether color-flavor locked (CFL) quark matter, modeled by the MIT bag model, can explain the observed properties of two compact stars, which have similar low masses but potentially different radii. The study explores two scenarios: absolutely stable strange quark matter and hybrid stars, determining acceptable ranges for the superconducting gap and bag parameter in each case. This work illustrates how observational constraints can discriminate between different realizations of quark matter in compact stars.Weak interactions play a crucial role in shaping the thermal and chemical evolution of compact stars and their progenitors. Kabir et al. investigate β-decay properties of medium-mass nuclei relevant for stellar environments, combining relativistic mean-field calculations of nuclear deformation with pn-QRPA evaluations of Gamow-Teller strength and stellar weak rates. The resulting rates, systematically larger than those obtained in alternative models, are of direct relevance for simulations of late-stage stellar evolution and nucleosynthesis. On a much larger astrophysical scale, Blaschke et al. address the long-standing puzzle of the near-universality of heavy-element abundances. Using a nonequilibrium freeze-out framework and a phenomenological characterization of r-process distributions, they show how weak-interaction-driven dynamics and density fluctuations can naturally account for both the typical abundance pattern and its observed variations.The macroscopic manifestations of dense-matter microphysics are further explored through studies of gravity and rotation. Cai and Li derive equation-of-state-independent constraints on supradense matter by analyzing the scaled Tolman-Oppenheimer-Volkoff equations in general relativity. This work reveals tight bounds on the pressure-energy-density ratio and establishes direct links between observable neutron star properties and the dense matter EoS, without reliance on specific nuclear models. Farrell et al. examine the effects of differential rotation and finite temperature on neutron star structure and stability, using finite-temperature relativistic Brueckner-Hartree-Fock equations of state. The results demonstrate that differential rotation has a significant impact on maximum masses and rotational instabilities, while temperature plays a comparatively minor role within the explored range. These findings are particularly relevant for interpreting post-merger remnants.Combined, the articles collected in this Research Topic illustrate the rich and multifaceted role of strong and weak interactions in compact stars, from the microphysics of nuclei and quarks to the global structure and dynamics of general-relativistic, rotating objects. They underscore the necessity of combining microscopic theory, phenomenological modeling, and observational input to make progress in this field. We hope that this collection will serve both as a highlight of current advances and as a stimulus for future work aimed at unraveling the physics of matter under extreme conditions.