Exploding radiating viscous spheres in general relativity

The influence of viscosity on the gravitational collapse in radiating fluid spheres is investigated. The interior solution is matched with the Vaidya metric at the boundary of the fluid distribution. Prescribing an equation of state to take into account the degree of induced anisotropy by the viscosity and using the Herrera, Jiménez and Ruggeri method, we obtain an explicit Tolman VI-like exploding model. The sphere explodes more violently when the anisotropy due to the viscosity is smaller. The shear viscosity diminishes with the expansion of the distribution of matter.     

Luminosity profiles and the contraction of radiating spheres in general relativity

A semi-numeric method by Herrera, Jiménez and Ruggeri is used to study the evolution of general relativistic spheres in the free streaming radiation approximation when specific contraction schemes are imposed and for particular oscillatory radiation profiles. On one hand, the emerging radiation is studied for oscillating contracting spheres, on the other, the variation of the boundary surface is analyzed when a pulsating profile is provided. We considered three particular equations of state previously studied. It is found that the oscillatory frequency of the surface for the equations of state considered coincide with the frequency of the oscillation for the radiation profile.     

Cosmological mass model in general relativity

Relativistic cosmological field equations are obtained for a non-static stationary Bertotti-Robinson-type space-time for interacting perfect fluid and electromagnetic field. The cosmological solution to the field equations are obtained and the nature of the electromagnetic field as well the perfect fluid are studied. The electromagnetic field generated here corresponds to a special generic case and the perfect fluid distribution degenerates into a barotropic perfect fluid with equation of statep+=0, >0. It is shown here that the interacting barotropic fluid can generate gravitation only when the cosmological constant being a function ofx in a dynamic field.     

A magnetized homogeneous inflationary cosmological model in general relativity

In this paper we have investigated the effect of magnetic field on an orthogonal Bianchi type-I inflationary cosmological model using the concept of Higgs field. It has been investigated that the expansion and inflation in the model increases as the magnetic field increases. To get inflationary model we have assumed a mass less scalar field with flat potential V(φ)that has flat region. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kaluza-Klein radiating model in a general scalar-tensor theory

A five dimensional Kaluza-Klein space-time is considered in the presence of prefect fluid source in the general scalar-tensor theory of gravitation proposed by Nordtvedt (Astrophys. J. 161:1069, 1970) with the help of special law of variation for Hubble’s parameter given by Bermann (Nuovo Cimento 74B:182, 1983). A cosmological model with a negative constant deceleration parameter is obtained in this theory. Some physical properties of the model are also discussed.     

Retraction Note to: Luminosity profiles and the contraction of radiating spheres in general relativity

Astrophysics and Space Science - We report a model study on the effects of clouds on emission spectra of super-Venus planets. Our goal is to assess possible ways to identify characteristic spectral...     

FLRW non-singular cosmological model in general relativity

A singularity free cosmological model is obtained in a homogeneous and isotropic background with a specific form of the Hubble parameter in the presence of an interacting dark energy represented by a time-varying cosmological constant in general relativity.Different cases that arose have been extensively studied for different values of the curvature parameter.Some interesting results have been found with this form of the Hubble parameter to meet the possible negative value of the deceleration parameter(-1/3 q 0) as the current observations reveal.For some particular values of these parameters,the model reduces to Berman's model.     

Collapse of a radiating anisotropic star

Further results are obtained concerning the model of a collapsing anisotropic body by Kolassis and Santos. It is assumed an anisotropic equation of state for the static configuration, and a relation between the radiation density and heat flux. The total luminosity received by an observer at infinity is independent of the anisotropy of the fluid and of the radiation produced in the body. Numerical calculations are performed for a body having a mass of 5M in order to obtain the effective adiabatic index.     

The inflationary Kantowski-Sachs cosmological model in general relativity

In this paper, we have investigated the inflationary Kantowski-Sachs cosmological model in the presence of mass less scalar field with a flat potential. To get an inflationary solution, we have considered a flat region of a constant potential V. Some physical and kinematical properties of the model are studied.     

Revisiting the classical electron model in general relativity

Motivated by earlier studies (Tiwari et al. in Astrophys. Space Sci. 182:105, 1984; Herrera and Varela in Phys. Lett. 189:11, 1994), we model electron as a spherically symmetric charged perfect fluid distribution of matter. The existing model is extended assuming a matter source that is characterized by quadratic equation of state in the context of general theory of relativity. For the suitable choices of the parameters, our charged fluid models almost satisfy the physical properties of electron.     

Magnetostatic stiff-fluid model of cylindrical symmetry in general relativity

We study the static stiff-fluid model for perfect fluid distributions in the presence of incident magnetic field. The magnetic field is surrounded by static stiff fluid of infinite electric conductivity and it is due to the electric current flowing along theZ-axis. The various physical and geometrical properties together with the state of model in absence of magnetic field are also discussed.     

On slowly-rotating cosmological viscous-fluid model universes in general relativity

The dynamics of a slowly-rotating cosmological viscous-fluid universe is investigated and the rotational perturbations of such models are studied in order to substantiate the possibility that the Universe is endowed with slow rotation, in the course of presentation of some new analytic solutions. Three different cases are taken up in which the nature and role of the metric rotation (r, t) as well as that of the matter rotation (r, t) are discussed. The periods of physical validity of some of the models and the effect of viscosity on the rotational motion are also found out. Rotating models which are expanding as well are obtained, where in all the cases the rotational velocities are found to decay with the time; and these models may be taken as good examples of real astrophysical situations.     

Bianchi Type-III stiff fluid cosmological model in general relativity

In this paper, we have investigated a tilted Bianchi Type-III stiff fluid cosmological model in general relativity. To get a determinate solution, we have assumed a condition A=(BC) ⁿ between metric potentials. The various physical and geometrical aspects of the model are discussed.     

Magneto-viscous fluid cosmological model of plane symmetry in general relativity

The object of this paper is to investigate the behaviour of magnetic field in a viscous fluid cosmological model. Various physical and geometrical properties of the model have also been discussed.     

Expanding and shearing magneto-viscous fluid cosmological model in general relativity

The object of this paper is to investigate the behavior of a magnetic field in a viscous fluid cosmological model. It has been assumed that the expansion () is proportional to the eigenvalue ₁ of the shear tensor _i ^j and the coefficient of shearing viscosity is proportional to the scalar of expansion. The paper also discusses the behavior of the model when the magnetic field tends to zero and comments on some other physical properties.     

Radiating anisotropic two-fluid model universes involving rotation in general relativity

Radiating anisotropic two-fluid model universes coupled with a scalar field when a slow rotation is introduced in them are studied here, where the anisotropic pressure is generated by the presence of two non-interacting perfect fluids which are in relative motion with respect to each other. Special discussion is made of the physically interesting class of models in which one fluid is a comoving radiative perfect fluid which is taken to model the cosmic microwave background and the second a non-comoving perfect fluid which will model the observed material content of the Universe. Here we take up four analytic solutions. The effects of rotation on these models are studied and the reactions of the scalar and the radiation fields with respect to the rotational motion are discussed. Analysis on the rotational perturbations are also made, in the course of which the amount of anisotropy induced in the pressure distribution by a small deviation from the Friedmann metric is also investigated. It is shown that such anisotropies could grow faster than the expansion of the Universe. The rotating models we obtain here are found to be theoretically satisfactory and they may be taken as physically acceptable models.     

Comments on revisiting the classical electron model in general relativity

We point out here that all the solutions presented in Rahaman et al. (Astrophys. Space Sci. 331:191–197, 2011) are incorrect and do not satisfy the system of governing Einstein-Maxwell field equations.     

A gravitationally non-degenerate cosmological model with expanding and shearing viscous fluid in general relativity

The object of this paper is to investigate the behaviour of viscosity in a cosmological model, in which the coefficient of shear viscosity is assumed to be proportional to rate of expansion in the model. The behaviour of the model in the absence of shear viscosity is also discussed.