The rotating neutron-star properties are studied to investigate a phase transition to quark matter. The density-dependent relativistic mean-field model (DD-RMF) is employed to study the hadron matter, while the vector-enhanced bag (vBag) model is used to study the quark matter. The star-matter properties such as mass, radius, the moment of inertia, rotational frequency, Kerr parameter, and other important quantities are studied to see their effect on quark matter. The maximum mass of a rotating neutron star with the DD-LZ1 and DD-MEX parameter sets is found to be around $3M_{\odot }$ for pure hadronic phase and decreases to around $2.6M_{\odot }$ upon phase transitioning to quark matter, which satisfies the recent GW190814 possible maximum mass constraint, implying that the secondary component of GW190814 could be a fast-rotating hybrid star. For DDV, DDVT, and DDVTD parameter sets, the maximum mass decreases to satisfy $2M_{\odot }$. The moment of inertia calculated for various DD-RMF parameter sets decreases with the increasing mass satisfying constraints from various measurements. Other important quantities calculated also vary with the bag constant and hence show that the presence of quarks inside neutron stars can also allow us to constraint these quantities to determine a proper equation of state. Also, the theoretical study along with the accurate measurement of uniformly rotating neutron-star properties may offer some valuable information concerning the high-density part of the equation of state.

We investigate the peculiar nature of strange stars through an analysis of different quark models, i.e. vBag model and CFL model equation of states at different parameter sets, and focus on understanding the equation of state governing the intriguing central compact object (CCO) within the supernova remnant HESS J1731-347, with a mass and radius of $$M = 0.77^{+0.20}_{-0.17} M_{\odot }$$M = 0 . 77 - 0.17 + 0.20 M ⊙ and $$R = 10.4^{+0.86}_{-0.78}$$R = 10 . 4 - 0.78 + 0.86 km, respectively. Additionally, we compare the radial oscillations of two models to determine the frequency of the HESS J1731-347 compact object at its maximum mass. The frequencies of radial oscillations are computed for each of the four EoSs considered. In total, the 10 lowest radial frequencies for each of those EoSs have been computed. By delving into these aspects, we aim at deepening our understanding of strange stars and their connection to the observed HESS J1731-347 mass-radius relationship.

We systematically study the properties of pure nucleonic and hyperonic magnetic stars using a density-dependent relativistic mean-field (DD-RMF) equations of state. We explore several parameter sets and hyperon coupling schemes within the DD-RMF formalism. We focus on sets that are in better agreement with nuclear and other astrophysical data while generating heavy neutron stars. Magnetic field effects are included in the matter equation of state and in general relativity solutions, which in addition fulfill Maxwell’s equations. We find that pure nucleonic matter, even without magnetic field effects, generates neutron stars that satisfy the potential GW 190814 mass constraint; however, this is not the case for hyperonic matter, which instead only satisfies the more conservative 2.1 M _⊙ constraint. In the presence of strong but still somehow realistic internal magnetic fields ≈10¹⁷ G, the stellar charged particle population re-leptonizes and de-hyperonizes. As a consequence, magnetic fields stiffen hyperonic equations of state and generate more massive neutron stars, which can satisfy the possible GW 190814 mass constraint but present a large deformation with respect to spherical symmetry.

We determine parameters of the renormalization group-consistent three-flavor color-superconducting Nambu–Jona-Lasinio (NJL) model that are suited to investigate possible compact-star configurations. Our goal is to provide quark-matter equations of state (EOSs) that can be used for hadron-quark hybrid-star constructions. To that end, we mainly focus on the parameters of the quark-matter model. By varying the vector and diquark coupling constants, we analyze their impact on the EOS, the speed of sound, the maximum diquark gap, and the mass-radius relation. In almost all configurations, a stable color-flavor-locked (CFL) phase appears in the core of the maximum-mass configurations, typically spanning several kilometers in radius. In other cases, the star’s two-flavor color-superconducting (2SC) branch of the EOS becomes unstable before reaching the CFL transition density. At neutron-star densities, the speed of sound squared reaches up to c s 2 ∼ 0.6 and the CFL gap up to Δ ∼ 250 MeV . We argue that adding a hadronic EOS at lower densities by performing a Maxwell construction does not increase the maximum mass substantially. Thus we use the 2.0 M ⊙ constraint to constrain the NJL model parameters that are suited for the construction of hybrid-star EOS. We construct three examples of the hybrid-star model, demonstrating that there is room for different color-superconducting compositions. The hybrid EOSs obtained in this way can have no 2SC matter or different ratios of 2SC and CFL quark matter in the core. We show that early hadron-quark transitions are possible that can modify the tidal deformability at 1.4 M ⊙ . We find that these EOSs are consistent with the imposed constraints from astrophysics and perturbative QCD. They allow for different hybrid-star scenarios with a hadronic EOS that is soft at low to intermediate densities ( ∼ 1 – 3 n sat ). Published by the American Physical Society 2025

We investigate the effect of $\mathrm{\Delta }$ baryons on the radial oscillations of neutron and hyperon stars, employing a density-dependent relativistic mean-field model. The spin-$3/2$ baryons are described by the Rarita-Schwinger Lagrangian density. The baryon-meson coupling constants for the spin-$3/2$ decuplet and the spin-$1/2$ baryonic octet are calculated using a unified approach relying on the fact that the Yukawa couplings present in the Lagrangian density of the mean-field models must be invariant under the SU(3) and SU(6) group transformations. We calculate the 20 lowest eigenfrequencies and corresponding oscillation functions of $\mathrm{\Delta }$-inclusive nuclear ($\mathrm{N}+\mathrm{\Delta }$) and hyperonic matter ($\mathrm{N}+\mathrm{H}+\mathrm{\Delta }$) by solving the Sturm-Liouville boundary value problem and also verifying its validity. We see that the lowest mode frequencies for $\mathrm{N}+\mathrm{\Delta }$ and $\mathrm{N}+\mathrm{H}$ EoSs are higher as compared to the pure nucleonic matter because of the deltas and hyperons present. Furthermore, the separation between consecutive modes increases with the addition of hyperons and $\mathrm{\Delta }$s.