Modified Gauge Invariant Einstein Maxwell Gravity and Stability of Spherical perfect fluid Stars with Magnetic Monopoles

TL;DR

This paper explores a modified Einstein-Maxwell gravity model with gauge invariance, analyzing the stability of spherical perfect fluid stars with magnetic monopoles, and finds conditions for their stability and physical viability.

Contribution

It introduces a gauge-invariant extension of Einstein-Maxwell gravity with directional coupling, and applies it to analyze the stability of magnetized stellar objects with a new approach.

Findings

Stable solutions for positive polytropic index a>0

Quasi-stable solutions for negative a<0

Energy conditions and stability criteria are satisfied

Abstract

As an alternative gravity model we consider an extended Einstein-Maxwell gravity containing a gauge invariance property. Extension is assumed to be addition of a directional coupling between spatial electromagnetic fields with the Ricci tensor. We will see importance of the additional term in making a compact stellar object and value of its radius. As an application of this model we substitute ansatz of magnetic field of a hypothetical magnetic monopole which has just time independent radial component and for matter part we assume a perfect fluid stress tensor. To obtain spherically symmetric internal metric of the perfect fluid stellar compact object we solve Tolman-Oppenheimer-Volkoff equation with a polytropic form of equation of state as $p(\rho)=a\rho^2$. Using dynamical system approach we study stability of the solutions for which arrow diagrams show saddle (quasi stable) for $a<0$ (dark stars) and sink (stable) for $a>0$ (normal visible stars). We check also the energy conditions, speed of sound and Harrison-Zeldovich-Novikov static stability criterion for obtained solution and confirm that they make stable state.