Charged Strange Quark Stars Research Articles

Charged compact stars with color–flavor-locked strange quark matter in f(R,T) gravity

Due to the high density of neutron stars, there is still an open question on the complete structure of the inner core of compact object. It is a great challenge to propose a model describing the highly-dense matter of neutron stars since there are neither experimentally nor observationally adequate results. In theoretical physics, Quantum Chromodynamics (QCD) predicts that at high densities and low temperatures the inner core of neutron stars could be made of exotic quark matter in the color-flavor-locked (CFL) phase of color superconductivity. Regarding the equation-of-state, we predict the existence of electrically charged strange quark stars in the background of the modified theory of gravity f(R,T). In our discussion, we assume a linear relation between charge density and the fluid energy density, and also utilize the f(R,T)=R+2βT model to numerically compute the generalized Tolman–Oppenheimer–Volkoff (TOV) structure equations. In order to compute the properties of quark stars, we discuss the mass–radius profile, the effect of the charge in the stellar interior, factor of compactness, and mass-central energy density relation for stellar stability. Finally, we provide a set of basic differences between the standard Einstein-Maxwell gravity and the modified f(R,T) gravity theory.

Maximum mass of anisotropic charged strange quark stars in a higher dimensional approach (D ≥ 4)

In this article, a new class of solutions of Einstein-Maxwell field equations of relativistic strange quark stars obtained in dimensions , is shown. We assume that the geometry of space-time is pseudo-spheroid, embedded in Euclidean space of dimensions. The MIT bag model equation of state is employed to study the relevant properties of strange quark stars. For the causal and non-negative nature of the square of the radial sound velocity , we observe that some restrictions exist on the reduced radius , where R is a parameter related to the curvature of the space-time, and b is the radius of the star. The spheroidal parameter λ used here defines the metric potential of the component, which is pseudo-spheroidal in nature. We note that the pressure anisotropy and charge have some effects on λ. The maximum mass for a given surface density () or bag constant assumes a maximum value in dimension and decreases for other values of D. The generalized Buchdahl limit for a higher dimensional charged star is also obeyed in this model. We observe that in this model, we can predict the mass of a strange quark star using a suitable value of the electric charge (Q) and bag constant (B). Energy and stability conditions are also satisfied in this model. Stability is also studied considering the dependence of the Lagrangian perturbation of radial pressure () on the frequency of normal modes of oscillations. The tidal Love number and tidal de-formability are also evaluated.

Electrically charged compact stars with an interacting quark equation of state

We investigate the properties of non-rotating, electrically charged strange quark stars in four-dimensional Einstein–Maxwell theory. For quark matter we adopt the well-motivated quantum chromodynamics (QCD) equation-of-state, while for the charge density we assume it is proportional to the mass density. The system of coupled structure equations are integrated numerically, and we compute the mass, the radius as well as the total electric charge of the stars. Moreover, we perform a detailed numerical study of the effect of electric charge using the interacting quark equation-of-state. We find that stars as heavy as two solar masses can be supported, and that the highest radius and highest mass of the stars increase with the charge density.

Electrically charged strange stars with an interacting quark matter equation of state

The properties of electrically charged strange quark stars predicted by an interacting quark matter equation of state (EoS) based on cold and dense perturbative quantum chromodynamics (pQCD) are investigated. The stability of strange stars is analyzed considering different models for the electric charge distribution inside the star as well as for distinct values for the total electric charge. A comparison with the predictions derived using the MIT bag model is also presented. We show that the presence of a net electric charge inside strange stars implies in a larger maximum mass in comparison to their neutral counterparts. Moreover, we demonstrate that the pQCD EoS implies larger values for the maximum mass of charged strange stars, with very heavy charged stars being stable systems against radial oscillations. For an electric charge distribution given by $q(r) = \beta r^3$, the pQCD EoS implies unstable configurations for large values of the renormalization scale as well as for large values of $\beta$, in contrast to the MIT bag model predictions.

Electrically charged strange quark stars with anisotropic matter: exact analytical solution

We obtain a new exact analytical solution to the Einstein–Maxwell field equations with anisotropic matter. The solution describes the interior of anisotropic, electrically charged strange quark stars with a non-linear equation-of-state. We show the behavior of the solution graphically, and we determine the properties of the star (radius, mass, electric charge and compactness) for specific numerical values of the parameters involved. Finally, we check that causality is not violated, and that the energy conditions, the upper bound on the compactness of the stars, and constraints on the mass of the objects coming from observed massive pulsars and direct detection of gravitational waves are all fulfilled.

Study on charged strange stars in f(R, T) gravity

We investigate the effects of the modified f(R, T) gravity on the charged strange quark stars with the standard choice of f(R, T)=R+2χ T. Those types of stars are supposed to be made of strange quark matter (SQM) whose distribution is governed by the phenomenological MIT bag EOS as p=1/3(ρ−4B), where B is the bag constant, while the form of charge distribution is chosen to be q(r)=Q(r/ℛ)3=α r3 with α as a constant. We derive the values of the unknown parameters by matching the interior spacetime to the exterior Reissner-Nordstr{öm metric followed by the appropriate choice of the values of the parameters χ and α. Our study reveals that besides SQM, a new kind of matter distribution originates due to the interaction between the matter and the extra geometric term, while the modification of the Tolman-Oppenheimer-Volkoff (TOV) equation invokes the presence of a new force Fc. The accumulation of the electric charge distribution reaches its maximum at the surface, and the predicted values of the corresponding electric charge and electric field are of the order of 1019−20C and 1021−22 V/cm, respectively. To examine the physical validity of our solutions, we perform tests of the energy conditions, stability against the equilibrium of the forces, the adiabatic index, etc., and find that the proposed f(R, T) model survives all these critical tests. Therefore, our model can describe the non-singular charged strange stars and justify the supermassive compact stellar objects having their masses beyond the maximum mass limit for the compact stars in the standard scenario. Our model also supports the existence of several exotic astrophysical objects like super-Chandrasekhar white dwarfs, massive pulsars, and even magnetars, which remain unexplained in the framework of General Relativity (GR).

Electrically charged strange quark stars with a non-linear equation-of-state

The properties of electrically charged strange quark stars are investigated. We assume a non-linear equation-of-state, and we obtain numerical solutions to the structure equations. The key features of the solutions obtained here are (i) they can support a 2 solar masses star, (ii) both the mass and the electric charge of the stars increase with the alpha parameter characterizing the electric density, (iii) the electric object is heavier and larger than its neutral counterpart.

A realistic model for charged strange quark stars

We report a general approach to solve an Einstein-Maxwell system to describe a static spherically symmetric anisotropic strange matter distribution with linear equation of state in terms of two generating functions. It is examined by choosing Tolmann IV type potential for one of the gravitational potentials and a physically reasonable choice for the electric field. Hence, the generated model satisfies all the required major physical properties of a realistic star. The effect of electric charge on physical properties is highlighted.

Radial oscillations of charged strange stars

The radial oscillations of charged strange quark stars is investigated. It is considered that the fluid pressure follows the MIT bag model equation of state and the charge density to be proportional to the energy density, ρe = αρ (where α is proportionality constant). The modified equations of radial oscillations to the introduction of the electric charge are integrated to determine the fundamental mode. It is found that the stability of the charged object decreases with the increment of the central energy density and with the growth of the charge fraction.

Equilibrium and stability of charged strange quark stars

The hydrostatic equilibrium and the stability against radial perturbation of charged strange quark stars composed of a charged perfect fluid are studied. For this purpose, it is considered that the perfect fluid follows the MIT bag model equation of state and the radial charge distribution follows a power-law. The hydrostatic equilibrium and the stability of charged strange stars are investigated through the numerical solutions of the Tolman-Oppenheimer-Volkoff equation and the Chandrasekhar's pulsation equation, being these equations modified from their original form to include the electrical charge. In order to appreciably affect the stellar structure, it is found that the total charge should be of order $10^{20}[\rm C]$, implying an electric field of around $10^{22}[\rm V/m]$. We found the electric charge that produces considerable effect on the structure and stability of the object is close to the star's surface. We obtain that for a range of central energy density the stability of the star decreases with the increment of the total charge and for a range of total mass the electric charge helps to grow the stability of the stars under study. We show that the central energy density used to reach the maximum mass value is the same used to determine the zero eigenfrequency of the fundamental mode when the total charge is fixed, thus indicating that the maximum mass point marks the onset of instability. In other words, when fixing the total charge, the conditions $\frac{dM}{d\rho_c}>0$ and $\frac{dM}{d\rho_c}<0$ are necessary and sufficient to determine the stable and unstable equilibrium configurations regions against radial oscillations.

Cylinder with charged anisotropic source

In this study, we consider a charged anisotropic fluid cylinder with no external pressure acting on the fluid. This is a cylindrical version of Krori and Barua’s method to explore the field equations with an anisotropic fluid. We discuss models with positive matter density and pressure that satisfy all of the energy and stability conditions. It is found that charge does not vanish at the center of the cylinder. The equilibrium condition as well as the physical conditions are discussed. Further, we highlight the connection between our solutions and charged strange quark stars and dark matter including charged massive particles. A graphical analysis of the matter variables versus charge is given, which indicates a physically reasonable matter distribution.

Charged anisotropic matter with linear or nonlinear equation of state

Ivanov pointed out substantial analytical difficulties associated with self-gravitating, static, isotropic fluid spheres when pressure explicitly depends on matter density. Simplification achieved with the introduction of electric charge were noticed as well. We deal with self-gravitating, charged, anisotropic fluids and get even more flexibility in solving the Einstein-Maxwell equations. In order to discuss analytical solutions we extend Krori and Barua's method to include pressure anisotropy and linear or non-linear equations of state. The field equations are reduced to a system of three algebraic equations for the anisotropic pressures as well as matter and electrostatic energy densities. Attention is paid to compact sources characterized by positive matter density and positive radial pressure. Arising solutions satisfy the energy conditions of general relativity. Spheres with vanishing net charge contain fluid elements with unbounded proper charge density located at the fluid-vacuum interface. Notably the electric force acting on these fluid elements is finite, although the acting electric field is zero. Net charges can be huge ($10^{19}\,C$) and maximum electric field intensities are very large ($10^{23}-10^{24}\,statvolt/cm$) even in the case of zero net charge. Inward-directed fluid forces caused by pressure anisotropy may allow equilibrium configurations with larger net charges and electric field intensities than those found in studies of charged isotropic fluids. Links of these results with charged strange quark stars as well as models of dark matter including massive charged particles are highlighted. The van der Waals equation of state leading to matter densities constrained by cubic polynomial equations is briefly considered. The fundamental question of stability is left open.

Electrically charged strange quark stars

The possible existence of compact stars made of absolutely stable strange quark matter--referred to as strange stars--was pointed out by Witten almost a quarter of a century ago. One of the most amazing features of such objects concerns the possible existence of ultrastrong electric fields on their surfaces, which, for ordinary strange matter, is around 10{sup 18} V/cm. If strange matter forms a color superconductor, as expected for such matter, the strength of the electric field may increase to values that exceed 10{sup 19} V/cm. The energy density associated with such huge electric fields is on the same order of magnitude as the energy density of strange matter itself, which, as shown in this paper, alters the masses and radii of strange quark stars at the 15% and 5% levels, respectively. Such mass increases facilitate the interpretation of massive compact stars, with masses of around 2M{sub {center_dot}}, as strange quark stars.