In this work we study the effects of strong magnetic fields on hybrid stars by using a full general-relativity approach, solving the coupled Maxwell–Einstein equation in a self-consistent way. The ...magnetic field is assumed to be axisymmetric and poloidal. We take into consideration the anisotropy of the energy–momentum tensor due to the magnetic field, magnetic field effects on equation of state (EoS), the interaction between matter and the magnetic field (magnetization), and the anomalous magnetic moment of the hadrons. The EoS used is an extended hadronic and quark SU(3) non-linear realization of the sigma model that describes magnetized hybrid stars containing nucleons, hyperons, and quarks. According to our results, the effects of the magnetization and the magnetic field on the EoS do not play an important role on global properties of these stars. On the other hand, the magnetic field causes the central density in these objects to be reduced, inducing major changes in the populated degrees of freedom and, potentially, converting a hybrid star into a hadronic star.
Aims. The Quark-Hadron Chiral Parity-Doublet model is applied to calculate compact star properties in the presence of a deconfinement phase transition. Methods. Within this model, a consistent ...description of nuclear matter properties, chiral symmetry restoration, and a transition from hadronic to quark and gluonic degrees of freedom is possible within one unified approach. Results. We find that the equation of state obtained is consistent with recent perturbative quantum chromodynamics results and is able to accommodate observational constraints of massive and small neutron stars. Furthermore, we show that important features of the equation of state, such as the symmetry energy and its slope, are well within their observational constraints.
With the computational power and algorithmic improvements available today, the ongoing STAR/RHIC and HADES/GSI experiments, the future FAIR and NICA facilities becoming operational, and the new ...precise measurements from NICER and LIGO/VIRGO, the high-energy nuclear physics and astrophysics communities are in the unique position to set very stringent constraints on the equation of state of strongly interacting matter. Here, we review the state-of-the-art of different approaches used in the description of hot and ultradense baryonic matter in and out of equilibrium, and discuss the regions in the phase diagram where heavy-ion collisions and neutron star mergers can overlap. Future perspectives are discussed to help define a comprehensive, multi-disciplinary strategy to map out the phase diagram of strongly interacting matter from heavy ion collisions to neutron stars.
A hadronic chiral SU(3) model is applied to neutron and proto-neutron stars, taking into account trapped neutrinos, finite temperature, and entropy. The transition to the chirally restored phase is ...studied, and global properties of the stars such as minimum and maximum masses and radii are calculated for different cases. In addition, the effects of rotation on neutron star masses are included, and the conservation of baryon number and angular momentum determines the maximum frequencies of rotation during the cooling.
ABSTRACT
We report a new equation of state (EoS) of cold and hot hyperonic matter constructed in the framework of the quark–meson-coupling (QMC-A) model. The QMC-A EoS yields results compatible with ...available nuclear physics constraints and astrophysical observations. It covers the range of temperatures from T = 0 to 100 MeV, entropies per particle S/A between 0 and 6, lepton fractions from YL = 0.0 to 0.6, and baryon number densities nB = 0.05–1.2 fm−3. Applications of the QMC-A EoS are made to cold neutron stars (NSs) and to hot proto-neutron stars (PNSs) in two scenarios: (i) lepton-rich matter with trapped neutrinos (PNS-I) and (ii) deleptonized chemically equilibrated matter (PNS-II). We find that the QMC-A model predicts hyperons in amounts growing with increasing temperature and density, thus suggesting not only their presence in PNS but also, most likely, in NS merger remnants. The nucleon–hyperon phase transition is studied through the adiabatic index and the speed of sound cs. We observe that the lowering of (cs/c)2 to and below the conformal limit of 1/3 is strongly correlated with the onset of hyperons. Rigid rotation of cold and hot stars, their moments of inertia and Kepler frequencies are also explored. The QMC-A model results are compared with two relativistic models, the chiral mean field model (CMF), and the generalized relativistic density functional (GRDF) with DD2 (nucleon-only) and DD2Y-T (full baryon octet) interactions. Similarities and differences are discussed.
Abstract
In this work, we study the effects of magnetic fields on hot white dwarfs. We model their interior as a nuclei lattice surrounded by a relativistic free Fermi gas of electrons, accounting ...for effects from temperature, Landau levels, and anomalous magnetic moment. We find that, at low densities (corresponding to the outer regions of star), both temperature and magnetic field effects play an important role in the calculation of microscopic thermodynamical quantities. To study macroscopic stellar structures within a general-relativistic approach, we numerically solve the coupled Einstein–Maxwell equations for fixed entropy per particle configurations and discuss how temperature affects stellar magnetic field profiles, masses, and radii.
In this work, we study the effects of magnetic fields and rotation on the structure and composition of proto-neutron stars. A hadronic chiral SU(3) model is applied to cold neutron stars and ...proto-neutron stars with trapped neutrinos and at fixed entropy per baryon. We obtain general relativistic solutions for neutron and proto-neutron stars endowed with a poloidal magnetic field by solving Einstein-Maxwell field equations in a self-consistent way. As the neutrino chemical potential decreases in value over time, this alters the chemical equilibrium and the composition inside the star, leading to a change in the structure and in the particle population of these objects. We find that the magnetic field deforms the star and significantly alters the number of trapped neutrinos in the stellar interior, together with strangeness content and temperature in each evolution stage.
Can magnetic fields (de)stabilize twin stars? Gomes, R O; Dexheimer, V; Han, S ...
Monthly notices of the Royal Astronomical Society,
06/2019, Letnik:
485, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Abstract
Sharp phase transitions allow for the existence of a third family of stable compact stars, twin stars. In this work, we investigate for the first time the role of strong magnetic fields on ...non-magnetic twin-star sequences and the case in which magnetic fields themselves give rise to a third family of stable stars. We use three sets of equations of state to study such effects from a general point of view. Magnetic field effects are introduced in the structure of stars through the solution of the Einstein-Maxwell equations, assuming a poloidal magnetic field configuration and a metric that allows for the description of deformed stars. We show that strong magnetic fields can destabilize twin-star sequences. On the other hand, magnetic fields can also give rise to twin stars in models that did not predict these sequences. In this sense, magnetic fields can play an important role in the evolution of neutron stars.
Heavy Magnetic Neutron Stars Rather, Ishfaq A.; Rahaman, Usuf; Dexheimer, V. ...
The Astrophysical journal,
08/2021, Letnik:
917, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
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 ≈10
17
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.
Abstract
The effects of strong magnetic fields on the deconfinement phase transition expected to take place in the interior of massive neutron stars are studied in detail for the first time. For ...hadronic matter, the very general density-dependent relativistic mean field model is employed, while the simple, but effective vector-enhanced bag model is used to study quark matter. Magnetic-field effects are incorporated into the matter equation of state and in the general-relativity solutions, which also satisfy Maxwell’s equations. We find that for large values of magnetic dipole moment, the maximum mass, canonical mass radius, and dimensionless tidal deformability obtained for stars using spherically symmetric Tolman–Oppenheimer–Volkoff (TOV) equations and axisymmetric solutions attained through the LORENE library differ considerably. The deviations depend on the stiffness of the equation of state and on the star mass being analyzed. This points to the fact that, unlike what was assumed previously in the literature, magnetic field thresholds for the approximation of isotropic stars and the acceptable use of TOV equations depend on the matter composition and interactions.
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