In this work, we study the properties of strange quark matter and reveal the evolution process of strange quark stars employing a self consistent thermodynamic treatment. A comprehensive and reliable thermodynamic basis for the study of the dynamic evolution from proto-strange quark stars to stable strange stars at a zero temperature is provided. The relative abundance of particles, equation of state, temperature, and mass-radius relationship at each stage of the evolution of stars are discussed, where the cold strange quark star are consistent with the observational mass and radius of Hess J1731-347, PSR J1231-1411, PSR J0030+0451, PSR J0348+0432, and PSR J0740+6620, which could be difficult to be explained by the standard neutron star model. A schematic diagram is provided as well, illustrating the state of different stages along the evolution of stars at a fixed baryon-mass.

Quarkyonic matter is expected to play a key role for the transition from hadronic matter to quark matter in compact stars. Within the framework of the relativistic mean-field model and equivparticle model with density-dependent quark masses, we construct the "quark Fermi sea" with a "baryon Fermi surface" to characterize the properties of the quarkyonic matter. In particular, we develop a comprehensive framework to account for the strangeness degrees of freedom, incorporating Lambda, Xi , and Sigma hyperons as well as strange quarks in a unified quarkyonic framework. Our calculations indicate that the inevitable emergence of hyperons softens the equations of state, leading to a reduction in the equilibrium sound velocity around nb 2n0, and consequently reducing the masses and radii of neutron stars. When the quark-hadron phase transition is taken into account, the equation of state at high densities exhibits additional softening consistent with current astronomical observational constraints. This softening leads to a maximum equilibrium sound velocity of vmax eq 0.6c, which is close to the ultrarelativistic limit of 0.58c.

Employing various relativistic energy density functionals for nucleon-nucleon interactions, we investigate the impact of hyperons and Δ resonances on the frequencies of non-radial oscillations in neutron stars, where the universal coupling scheme is adopted for the Δ-meson couplings. It is found that the inclusion of Δ resonances is essential for neutron stars to accommodate the recent mass and radius measurements of PSR J0030+0451, PSR J0740+6620, PSR J0437-4715, PSR J0614-3329, and HESS J1731-347. As Δ resonances start to emerge in neutron stars' inner core, the g-mode oscillation energy becomes concentrated within the Δ-admixed region, leading to a sharp increase in the g-mode frequency. We also examine the f-mode and p-mode oscillations and find that the impact of Δ resonances on these modes is less pronounced than the g-modes. The oscillation frequencies calculated in the Cowling approximation are then compared with those from full general relativity, confirming that the Cowling approximation introduces an error of approximately 20% for the f-modes and within 10% for the g-modes. The notable effect of Δ resonances on neutron stars' g-mode frequencies holds important implications for probing the internal composition of neutron stars.

We conduct a Bayesian inference study to systematically quantify how the precision of neutron-star radius measurements constrains relativistic mean-field (RMF) model parameters and the equation of state (EOS) of dense matter. Adopting the canonical radius constraint R_1.4 = 11.9 km with observational uncertainties σ = 1.0, 0.5, and 0.2 km, we find that high-precision data ( σ = 0.2 km) significantly tighten the constraints on the isoscalar couplings ( α _S and α _V ), thereby favoring a softer symmetric nuclear matter (SNM) EOS with lower pressures across all density functionals (DD-ME2, TW99, PKDD). In contrast, the constraints on the symmetry-energy-related coupling α _TV exhibit strong model dependence: uncertainties broaden for DD-ME2 and TW99 due to parameter-compensation effects under a softened EOS but narrow for PKDD owing to its stiffer symmetry-energy prior. This divergence propagates to the proton fraction and sound speed, where uncertainties increase for softer functionals but decrease for PKDD under high precision. Our results underscore that future radius measurements with σ≤ 0.2 km could decisively constrain high-density EOS behavior and disentangle the density dependence of nuclear matter properties, while also highlighting the critical role of low-density functional characteristics in Bayesian inference outcomes.

We investigate the properties of magnetized Coulomb crystals in neutron star crusts using a fully three-dimensional geometry with periodic boundary conditions. The electron density profiles are fixed via the Thomas-Fermi approximation, and the nonuniform magnetic fields are treated with the equivalent magnetic charge method. The study focuses on Coulomb crystals composed of ^12C at an ion number density n_d = 10^-9 fm^-3, subjected to various external magnetic fields. Nuclei are described by a Gaussian wave function, where the width b encapsulates the effects of zero-point ion vibrations and finite temperature. Our findings show that the crystal softens as b increases. The Madelung constant K_M fluctuates with the external magnetic field B_z0 at B_z0≤ 3× 10^14 G. At higher field strengths, K_M increases until B_z0≈ 3× 10^15 G and then decreases. The body-centered cubic (BCC) lattice is slightly more stable than the face-centered cubic (FCC) lattice when B_z0 < 3× 10^15 G, whereas the FCC lattice may become more stable at larger B_z0. The elastic constants c_11-c_12 and c_44 are computed and tabulated, which grow with B_z0 for 3× 10^14 G≲ B_z0≲ 2× 10^15 G and then decline toward zero as the field strength increases further. For B_z0≳ 10^16 G, it becomes difficult to identify a stable lattice structure. These results provide valuable insights into the role of strong magnetic fields in shaping the properties of Coulomb crystals in compact stars.

We perform a Bayesian inference of the equation of state (EOS) of cold dense matter within a density-dependent relativistic mean-field (DD-RMF) model. An explicit inverse-mapping procedure reconstructs the density-dependent couplings from a physically interpretable ten-dimensional parameter set while enforcing thermodynamic consistency together with stability and causality conditions. The EOS is constrained by complementary multi-messenger data including chiral effective field theory calculations at low density, heavy-ion collision flow information at intermediate densities, NICER mass-radius posteriors, and the existence of approximately two-solar-mass pulsars. The combined constraints strongly restrict both isoscalar and isovector sectors. In particular, the chiral effective field theory band favors a relatively soft symmetry-energy slope around 38 MeV, corresponding to a compact canonical neutron-star radius of about 11.6 km. To reconcile the intermediate-density softness suggested by heavy-ion data with the high-density stiffness required by massive pulsars, the posterior prefers a moderately large Dirac effective mass at saturation together with correlated high-density limits of the scalar and vector couplings. The resulting sound-speed profile remains causal and shows significant stiffening above the conformal limit at several times nuclear saturation density, indicating strongly interacting matter in neutron-star cores. Evidence diagnostics indicate strong compatibility among the adopted constraints within the present DD-RMF framework.

Data tables on the equation of state (EOS) and microscopic structures for cold dense stellar matter with proton fractions Y-p = 0.01-0.65 and baryon number densities n(b) = 10(-8)-2 fm(-3) are obtained adopting 13 different relativistic density functionals, i.e., NL3, PK1, PK1r, GM1, MTVTC, DD-LZ1, PKDD, DD-ME2, TW99, DD-MEX, DD-MEX1, DD-MEX2, and DD-MEY. The EOSs of dense stellar matter inside neutron stars with baryon number densities n(b) = 7.6 & times; 10(-11)-2 fm(-3) are obtained as well fulfilling beta-stability condition, where those with TW99, DD-MEY, DD-MEX1, DD-ME2, DD-MEX, and DD-LZ1 are generally consistent with the constraints obtained by Huth et al. [Nature (London) 606, 276 (2022)] at n(b) less than or similar to 0.19 fm(-3) and at larger densities only TW99 gives satisfactory predictions. In general, the dense stellar matter exhibits droplet phase at n(b) less than or similar to 0.015 fm(-3), while more exotic structures such as rods, slabs, tubes, and bubbles appear sequentially as density increases. The critical proton fractions Y-p(drip)(approximate to 0.26-0.31) for neutron drip are obtained, where neutron gas emerges outside of nuclei at Y-p < Y-p(drip). For dense stellar matter at small densities (n(b) less than or similar to 10(-5) fm(-3)) or large proton fractions (nb <= 0.1 fm(-3) and Y-p >= Y-p(drip)), the EOSs and microscopic structures are generally insensitive to the adopted density functionals. With the onset of neutron drip at Y-p less than or similar to Y-p(drip), the uncertainties emerge and peak at nb approximate to 0.02 fm(-3) within the range 10(-5) less than or similar to n(b) less than or similar to 0.1 fm(-3). At nb greater than or similar to 0.1 fm(-3), the dense stellar matter becomes uniform and muons eventually appear, where the uncertainties in the EOSs grow significantly.

We perform a systematic Bayesian analysis of quark star equations of state under current multimessenger constraints, investigating the impact of prior assumptions and extreme-mass observations. Quark matter is modeled within an interacting MIT bag framework that consistently accommodates color-superconducting phases (2SC, 2SC+s, and CFL) and perturbative QCD corrections. We find that quark star models exhibit a distinct advantage in naturally accommodating the ultra-low mass object HESS J1731-347, a configuration that is challenging for standard neutron star models. In the high-mass regime, the interpretation of the secondary component of GW190814 is shown to be strongly prior-dependent: only broad priors allow for the substantial stiffness required to support such a massive object (∼2.6 M_⊙), while more restrictive priors favor a softer equation of state consistent with standard pulsar populations. Microscopically, we demonstrate that current data tightly constrain the effective bag constant and the overall stiffness, but cannot distinguish between different color-superconducting phases. Furthermore, we validate a reduction of the model to two effective parameters without loss of information. Our results indicate that if quark stars exist, their sound speeds consistently exceeds the conformal limit (c_s^2>1/3) at stellar densities.

Following the previous wor k[1] here we consider early thermal evolution of hot strange stars made of color superconducting quarks in two different pairing states: two-flavor color superconductor (2SC) and color-flavor-locked (CFL) phases, taking into account cooling by neutrinos and electron-positron pair creation due to the Schwinger process. We show that Schwinger luminosity in the electrosphere is a universal function of temperature, independent of quark matter phase for quark chemical potential μ_q>280 MeV. The surface of a strange star in all the cases cools faster than its interior. This leads to a fast decrease of pair luminosity with time, so that it does not exceed 10^46 erg/s at 1 second after strange star formation. Neutrino luminosity dominates over pair luminosity in all the cases except for the CFL phase with a large gap parameter Δ>60 MeV, where there is a strong suppression of neutrino emission. The total energy emitted in electron-positron pairs is always smaller than the energy emitted in neutrinos, but they become comparable for the large gap parameter.

As density increases, the shape of nuclei transitions to nonspherical "nuclear pasta" structures. The physical properties of the nuclear pasta, such as thermal conductivity and elasticity, have implications for detecting continuous gravitational waves from a rapidly rotating neutron star. In this work, we investigate the effect of the nuclear pasta on the quadruple moment, and find out that, compared with previous work, the quadrupole moment contributing to continuous gravitational-wave radiation can be up to 2 orders of magnitude larger. We also discuss the relationship between the quadruple moment and the maximum shear strain. Considering the properties of nuclear pasta, we study the detectability of known accreting neutron stars and compare predicted results to the detectable amplitude limits. These sources are well above the sensitivity curves for Cosmic Explorer and Einstein Telescope detectors. Our work advances the understanding of the properties of nuclear pasta and a possible mechanism for continuous gravitational waves.

Data tables on the equation of state (EOS) and microscopic structures for cold dense stellar matter with proton fractions Y_p =0.01-0.65 and baryon number densities n_b=10^-8-2 fm^-3 are obtained adopting 13 different relativistic density functionals, i.e., NL3, PK1, PK1r, GM1, MTVTC, DD-LZ1, PKDD, DD-ME2, TW99, DD-MEX, DD-MEX1, DD-MEX2, and DD-MEY. The EOSs of dense stellar matter inside neutron stars with baryon number densities n_b=7.6× 10^-11-2 fm^-3 are obtained as well fulfilling β-stability condition. In general, the dense stellar matter exhibits droplet phase at n_b≲ 0.015 fm^-3, while more exotic structures such as rods, slabs, tubes, and bubbles appear sequentially as density increases. The critical proton fractions Y_p^drip (≈ 0.26-0.31) for neutron drip are obtained, where neutron gas emerges outside of nuclei at Y_p< Y_p^drip. For dense stellar matter at small densities (n_b≲ 10^-5 fm^-3) or large proton fractions (n_b≲0.1 fm^-3 and Y_p≳ Y_p^drip), the EOSs and microscopic structures are generally insensitive to the adopted density functionals. With the onset of neutron drip at Y_p≲ Y_p^drip, the uncertainties emerge and peak at n_b≈ 0.02 fm^-3 within the range 10^-5≲ n_b≲0.1 fm^-3. At n_b≳0.1 fm^-3, the dense stellar matter becomes uniform and muons eventually appear, where the uncertainties in the EOSs grow significantly.

Pulsar-like objects are extremely compact, with an average density that exceeds nuclear saturation density, where the fundamental strong interaction plays an essential role, particularly in the low-energy regime. The internal structures and properties of those objects are profoundly connected to phenomena such as supernova explosions, gamma-ray bursts (GRBs), fast radio bursts (FRBs), high/low-mass compact stars and even to issues like dark matter and cosmic rays. However, due to the nonperturbative nature of quantum chromodynamics (QCD), significant uncertainties remain in our current understanding of the composition and equation of state (EOS) for the dense matter inside them. Drawing on three-flavor symmetry and the strong coupling between light quarks, this paper presents a novel perspective on the nature of pulsars: they are actually composed of strange matter, in the form of either strange quark matter or strangeon (analogous to nucleons and representing multibaryon states with three-flavor symmetry) matter. As both strange quark matter and strangeon matter contain nonzero strangeness, we refer to them collectively as "strange matter", and to the corresponding compact stars as "strange stars". We then briefly introduce several physical models describing strange matter and present the resulting structures and properties of strange stars. This includes discussions on the EOSs, surface properties, mass-radius relations, glitches, binary compact star mergers and dark matter. Furthermore, we will explore how observational properties of pulsar-like objects support the strange star model.

Strange quark matter (SQM) is considered to be the true ground state of the strong interactions, but recent studies have shown that ordinary quark matter (u-d quark matter, u-d QM) may also be the ground state of the strong interactions. By inserting an attenuation factor of Woods-Saxon potential type into the quark mass scaling, the resulting calculations of equation of state of u-d QM based on equiv-particle model show that the stability window of model parameters for stable u-d QM can be significantly enlarged with proper model parameters, which can be seen in the following figure. In this figure, the red solid and dashed lines represent the curves of root D versus C with and without attenuation factor, respectively, when the minimum value of the average energy per baryon is set to 930 MeV; the blue solid and dashed lines represent the curves of root D versus C with and without attenuation factor, respectively, when m(u) = 0. Thereby, the red and blue shaded areas are the absolute stable regions of u-d QM without and with attenuation factor in mass scaling. It is obvious that with the attenuation factor and proper model parameters, the absolute stable region (blue shaded area) for u-d QM can be much larger than that without the attenuation factor (red shaded area). The introduction of the attenuation factor allows the maximum mass of ordinary quark star (u-d quark star, u-d QS) to be larger than twice the solar mass, while the tidal deformability satisfies Lambda(1.4) is an element of[70, 580], which is consistent with the current astronomical observations. Therefore, the pulsars may be essentially the u-d QSs. This result provides a possibility for understanding the nature of pulsars, and it also further deepens the understanding of the strong interactions. [GRAPHICS] .

Dynamical tides of neutron stars in the late stages of binary inspirals provide a viable probe into dense matter through gravitational waves and potentially trigger electromagnetic precursors. We model the tidal response as a set of driven harmonic oscillators, where the natural frequencies are given by the quasinormal modes of a nonrotating neutron star. These modes are calculated in general relativity by applying linear perturbation theory to stellar models that include a solid crust and compositional stratification. For the mode spectrum, we find that the canonical interface mode associated with crust-core boundary vanishes in stratified neutron stars and is replaced by compositional gravity modes with mixed gravity-interfacial character, driven primarily by strong buoyancy in the outer core. We also find that fluid modes such as the core gravity mode and the fundamental mode can penetrate the crust, and we establish a criterion for such penetration. Regarding the tidal interaction, we find that transfer of binding energy to oscillations is dominated by the fundamental mode despite its frequency being too high to resonate with the tidal forcing. In general, we find that lower-frequency modes induce gravitational-wave phase shifts smaller than ∼ 10 − 3 rad for the equation of state we consider. We discover that nonresonant fundamental and crustal shear modes can trigger crust breaking already near the first gravity-mode resonance, while gravity-mode resonance concentrates strain at the base of the crust and may marginally crack it. These results suggest that both resonant and nonresonant excitations can overstress the crust and may channel energy into the magnetosphere prior to merger, potentially powering electromagnetic precursors. Our work represents an important step toward realistic modeling of dynamical tides of neutron stars in multimessenger observations.

It was shown that light nuclei such as He-4, Be-8, and C-12 can be well described by RMF models, which enables a unified description for nuclei with baryon numbers A greater than or similar to 4. In this work, I propose a hybrid treatment for investigating the clustering phenomenon in nuclear medium, where clusters ranging from light nuclei (e.g., H-3, He-3, and He-4) to heavy ones (e.g., C-12, O-16, Ca-40, Ca-48, and Pb-208) can be treated in a unified manner. In particular, assuming a spherical Wigner-Seitz cell, the clusters are fixed by solving the Dirac equations imposing the Dirichlet-Neumann boundary condition, while the nuclear medium are treated with Thomas-Fermi approximation and take constant densities. In the presence of nuclear medium, the clusters eventually become unbound as density increases, while the root-mean-square charge radii increase. For clusters with different proton and neutron numbers N-p not equal N-n, their binding energies vary with the proton fraction of nuclear medium, which are less significant for clusters with N-p=N-n. The uncertainties of density functionals on the clustering phenomenon are investigated as well, adopting 8 different functionals. Based on the obtained results, an analytical formula describing the binding energies of in-medium clusters is then obtained. The results presented in this work should be useful to understand the clustering phenomenon in both heavy-ion collisions and neutron stars.

In this paper, we constrain the symmetry energy at high densities in nuclear matter using recent observations of neutron stars based on the calculations of relativistic mean-field models. Using the observations of the neutron stars, we obtain the constraint on the symmetry energy at high densities, S(2ρ _0) =40.54± 12.47 MeV, and S(3ρ _0) =44.12± 29.38 MeV.