Narrow Results

We use a modified SU(2) chiral sigma model to study nuclear matter at high density using mean field approach. We also study the phase transition of nuclear matter to quark matter in the interior of highly dense neutron stars. Stable solutions of Tolman–Oppenheimer–Volkoff equations representing hybrid stars are obtained with a maximum mass of 1.69M_⊙, radii around 9.3 km and a quark matter core constituting nearly 55–85% of the star radii.

We use a modified SU(2) chiral sigma model to study nuclear matter component and simple bag model for quark matter constituting a neutron star. We also study the phase transition of nuclear matter to quark matter with the mixed phase characterized by two conserved charges in the interior of highly dense neutron stars. Stable solutions of Tolman–Oppenheimer–Volkoff equations representing hybrid stars are obtained with a maximum mass of 1.67M_⊙ and radius around 8.9 km.

The properties of hybrid stars are studied via the hybrid EOSs that are compatible with astrophysical observables. These hybrid EOSs are constructed by interpolating between hadronic EOS at lower densities and the quark EOS at higher densities. The BSR6 EOS derived from the RMF model is adopted as the hadronic EOS, while the quark EOS is calculated via a quasiparticle model. The maximum masses obtained from the hybrid EOSs are larger than $2M_{\odot }$, and the tidal deformabilities for $1.4M_{\odot }$ hybrid stars are smaller than 800. The combined tidal deformability $\tilde{\mathrm{\Lambda }}$ is a monotonically increasing function of mass ratio $\eta$ for both hybrid EOSs and hadronic EOS, and it depends weakly on $\eta$. The results of all hybrid EOSs can strictly satisfy the constraint of $70<\tilde{\mathrm{\Lambda }}<720$ and the mass and radius constraints from the newest joint analysis of NICER, XMM-Newton and GW170817 data.

We analyze the magnetic field evolution in dense quark matter with unbroken chiral symmetry, which can be found inside quark and hybrid stars. The magnetic field evolves owing to the chiral magnetic effect in the presence of the electroweak interaction between quarks. In our study, we also take into account the magnetohydrodynamic turbulence effects in dense quark matter. We derive the kinetic equations for the spectra of the magnetic helicity density and the magnetic energy density as well as for the chiral imbalances. On the basis of the numerical solution of these equations, we find that turbulence effects are important for the behavior of small scale magnetic fields. It is revealed that, under certain initial conditions, these magnetic fields behave similarly to the electromagnetic flashes of some magnetars. We suggest that fluctuations of magnetic fields, described in frames of our model, which are created in the central regions of a magnetized compact star, can initiate magnetar bursts.

This article focuses on the two-flavor color superconducting phase at moderate baryon density. In order to simultaneously investigate the chiral phase transition and the color superconducting phase transition, the Nambu–Gorkov formalism is extended to treat the quark-antiquark and diquark condensates on an equal footing. The competition between the chiral condensate and the diquark condensate is analyzed. The cold dense charge neutral two-flavor quark system is investigated in detail. Under the local charge neutrality condition, the ground state of two-flavor quark matter is sensitive to the coupling strength in the diquark channel. When the diquark coupling strength is around the value obtained from the Fierz transformation or from fitting the vacuum bayron mass, the ground state of charge neutral two-flavor quark matter is in a thermal stable gapless 2SC (g2SC) phase. The unusual properties at zero as well as nonzero temperatures and the chromomagnetic properties of the g2SC phase are reviewed. Under the global charge neutrality condition, assuming the surface tension is negligible, the mixed phase composed of the regular 2SC phase and normal quark matter is more favorable than the g2SC phase. A hybrid nonstrange neutron star is constructed.

We study the strange quark mass effect on the phase diagram of strong interaction and the structure of compact stars with a thermodynamically enhanced perturbative QCD model by matching quark matter onto nuclear matter using the Gibbs conditions. It is found that the mass effect of strange quark matter can obviously stiffen the equation of state of mixed phases and result in more massive hybrid stars (HSs), while that usually lowers the maximum mass of pure quark stars. Given reasonable model parameters, the maximum mass of HSs can reach two times the solar mass and the stars always have mixed-phase core in a considerably wide range of model parameters.

The purpose of our work is to investigate some new features of a static anisotropic relativistic hybrid compact star composed of strange quark matter (SQM) in the inner core and normal baryonic matter distribution in the crust. Here we apply the simplest form of the phenomenological MIT bag model equation of state $p_q=\frac{1}{3}({\rho }_q-4B_g)$ to correlate the density and pressure of strange quark matter within the stellar interior, whereas radial pressure and matter density due to baryonic matter are connected by the simple linear equation of state $p_r=\alpha \rho -\beta$. In order to obtain the solution of the Einstein field equations, we have used the Tolman–Kuchowicz ansatz [R. C. Tolman, Static solutions of Einstein’s field equations for spheres of fluid, Phys. Rev.55 (1939) 364–373; B. Kuchowicz, Acta Phys. Pol.33 (1968) 541] and further derivation of the arbitrary constants from some physical conditions. Here, we examine our proposed model graphically and analytically in detail for physically plausible conditions. In particular, for this investigation, we have reported on the compact object Her $X-1$ [$\mathrm{\text{Mass}}=(0.98\pm 0.12)M_{\odot }$; $\mathrm{\text{Radius}}=8.1_{-0.41}^{+0.41}$ km] in our paper as a strange quark star candidate. In order to check the physical validity and stability of our suggested model, we have performed various physical tests both analytically and graphically, namely, dynamical equilibrium of applied forces, energy conditions, compactness factor and surface redshift. Finally, we have found that our present model meets all the necessary physical requirements for a realistic model and can be studied for strange quark stars (SQS).