Study of stellar structures in f(ℛ,𝒯μν𝒯μν) theory

This paper deals with the dynamics of cylindrical collapse with anisotropic fluid distribution in the framework of [Formula: see text] gravity. For this purpose, we consider non-static and static cylindrical spacetimes in the inner and outer regions of a star, respectively. To match both geometries at the hypersurface, we consider the Darmois junction conditions. We use the Misner–Sharp technique to examine the impacts of correction terms and effective fluid parameters on the dynamics of a cylindrical star. A correlation between the Weyl tensor and physical quantities is also developed. The conformally flat condition is not obtained due to the influence of anisotropic pressure and higher-order nonlinear terms. Further, we assume isotropic fluid and specific model of this theory which yields the conformally flat spacetime and inhomogeneous energy density. We conclude that the collapse rate reduces as compared to general relativity due to the inclusion of effective pressure and additional terms of this theory.

Dynamical Analysis of Charged Dissipative Cylindrical Collapse in Energy-Momentum Squared Gravity

This paper investigates the dynamics of charged cylindrical collapse with the dissipative matter configuration in f(R,TαβTαβ) theory. This newly formulated theory resolves the primordial singularity and provides feasible cosmological results in the early universe.Moreover, its implications occur in high curvature regime where the deviations of energy-momentum squared gravity from general relativity is confirmed. We establish dynamical and transport equations through the Misner–Sharp and Mu¨ler–Israel Stewart techniques, respectively. We then couple these equations to examine the impact of effective fluid parameters and correction terms on the collapsing phenomenon. A connection between the modified terms, matter parameters, and Weyl tensor is also developed. To obtain conformal flatness, we choose a particular model of this theory and assume that dust matter with zero charge leads to conformal flatness and homogenous energy density. We found that the modified terms, dissipative matter, and electromagnetic field reduce the collapsing phenomenon.

Charged cylindrical collapse in f(𝒢) gravity

The aim of this paper is to study the gravitational collapse of charged cylindrical star in [Formula: see text] gravity. For this purpose, we derive dynamical equations by applying Misner–Sharp formalism and examine the effects of effective pressure and charge on the collapse rate. We also construct a relationship between matter variables, Gauss–Bonnet (GB) terms, and the Weyl tensor. For the constant value of [Formula: see text], it is found that spacetime is conformally flat if and only if the energy density is homogeneous. We conclude that the rate of collapse slows down in [Formula: see text] gravity due to anti-gravitational effects.

Measuring the filamentary structure of interstellar clouds through wavelets

Context. The ubiquitous presence of filamentary structures in the interstellar medium asks for an unbiased characterization of their properties including a stability analysis. Aims. We propose a novel technique to measure the spectrum of filaments in any two-dimensional data set. By comparing the power in isotropic and anisotropic structures we can measure the relative importance of spherical and cylindrical collapse modes. Methods. Using anisotropic wavelets we can quantify and distinguish local and global anisotropies and measure the size distribution of filaments. The wavelet analysis does not require any assumptions on the alignment or shape of filaments in the maps, but directly measures their typical spatial dimensions. In a rigorous test program, we calibrate the scale dependence of the method and test the angular and spatial sensitivity. We apply the method to molecular line maps from magneto-hydrodynamic (MHD) simulations and observed column-density maps from Herschel observations. Results. When applying the anisotropic wavelet analysis to the MHD data, we find that the observed filament sizes depend on the combination of magnetic-field-dominated density–velocity correlations and radiative transfer effects. This can be exploited by observing tracers with different optical depth to measure the transition from a globally ordered large-scale structure to small-scale filaments with entangled field lines. The unbiased view to Herschel column-density maps does not confirm a universal characteristic filament width. The map of the Polaris Flare shows an almost scale-free filamentary spectrum up to the size of the dominating filament of about 0.4 pc. For the Aquila molecular cloud the range of filament widths is limited to 0.05–0.2 pc. The filaments in Polaris show no preferential direction in contrast to the global alignment that we trace in Aquila. Conclusions. By comparing the power in isotropic and anisotropic structures we can measure the relative importance of spherical and cylindrical collapse modes and their spatial distribution.

Charged bulk viscous cylindrical collapse in f(R) theory

In this paper, we investigate the dynamics of charged cylindrical stellar collapsing model filled with bulk viscous dissipative fluid in [Formula: see text] gravity. For this purpose, we formulate dynamical equations through Misner–Sharp technique and derive transport equation. Finally, we analyze the collapse rate by coupling the transport and dynamical equations. It is concluded that the collapse rate of charged cylindrical model slows down under the influence of dark source terms and matter variables.

Dissipative cylindrical collapse of a charged anisotropic fluid in f(R) gravity

This paper is devoted to investigating the cylindrical collapse of an anisotropic fluid in f(R) gravity. For this purpose, the viscous charged anisotropic fluid dissipating energy with heat flow and shear is assumed. We use the perturbation scheme to develop the dynamical equations for the variables that ultimately lead to the disturbance of the physical variables and the Starobinksy-like f(R) model chosen. The evolution of the matter variables is discussed with the help of these equations. It can be concluded that the range of dynamic instabilities depends on the field strength, density distribution, pressure, and the curvature term of the f(R) model. We find that our results of Newtonian and post-Newtonian regimes reduce asymptotically to general relativity solutions in the limiting case.

A Study of Charged Cylindrical Gravitational Collapse with Dissipative Fluid

The present works deals with gravitational collapse of cylindrical viscous heat conducting anisotropic fluid following the work of Misner and Sharp. Using Darmois matching conditions, the dynamical equations are derived and the effects of charge and dissipative quantities over the cylindrical collapse are analyzed. Finally, using the Miller-Israel-Steward causal thermodynamic theory, the transport equation for heat flux is derived and its influence on collapsing system has been studied.