Impact of f(R,T) gravity in evolution of charged viscous fluids

In this work, the evolution of spherically symmetric charged anisotropic viscous fluids is discussed in framework of [Formula: see text] gravity. In order to conduct the analysis, modified Einstein Maxwell field equations are constructed. Nonzero divergence of modified energy momentum tensor is taken that implicates dynamical equations. The perturbation scheme is applied to dynamical equations for stability analysis. The stability analysis is carried out in Newtonian and post-Newtonian limits. It is observed that charge, fluid distribution, electromagnetic field, viscosity and mass of the celestial objects greatly affect the collapsing process as well as stability of stars.

On the stability of (M theory) stars against collapse: Role of anisotropic pressures

Unitarity of evolution in gravitational collapses implies existence of macroscopic stable horizonless objects. With such objects in mind, we study the effects of anisotropy of pressures on the stability of stars. We consider stars in four or higher dimensions and also stars in M theory made up of (intersecting) branes. Taking the stars to be static, spherically symmetric and the equations of state to be linear, we study “singular solutions” and the asymptotic perturbations around them. Oscillatory perturbations are likely to imply instability. We find that nonoscillatory perturbations, which may imply stability, are possible if an appropriate amount of anisotropy is present. This result suggests that it may be possible to have stable horizonless objects in four or any higher dimensions, and that anisotropic pressures may play a crucial role in ensuring their stability.

Radial pulsation stability as a function of hydrogen abundance

We explore the radial (p-mode) stability of stars across a wide range of mass (0.2 < M < 50 M⊙), composition (0 < X < 0.7, Z = 0.001, 0.02), effective temperature, and luminosity. We identify the instability boundaries associated with low- to high-order radial oscillations (0 ⩽ n ⩽ 13). The instability boundaries are a strong function of both composition and radial order (n). The classical blue edge shifts to higher effective temperature and luminosity with decreasing hydrogen abundance. High-order modes are more easily excited and small islands of high radial-order instability develop, some of which correspond with real stars. Driving in all cases is by the classical κ-mechanism and, at high luminosity-to-mass ratio, strange-mode instability. We identify regions of parameter space where new classes of pulsating variable have recently or may, in future, be discovered. The majority of these are associated with reduced hydrogen abundance in the envelope.