Scalar perturbations of gravastar model in the presence of global monopole

Abstract

In this article, we present a theoretical and phenomenological study of the gravastar in the presence of a global monopole in teleparallel gravity, specifically

gravity. We have constructed the interior based on both the global monopole and the dark energy, and on the shell, we have taken the stiff matter equation of state. We studied the thin shell surrounding the gravastar using the Israel junction conditions and derived a sufficient condition for its stability. We determined the deflection angle around the gravastar using both Gauss-Bonnet topological methods and analytical Hamilton–Jacobi methods. We checked the shadow around the gravastar at the equator using the ray-tracing method. We have presented the null-geodesic equation as an initial-value problem and applied numerical methods to trace the rays around the gravastar, also illustrating the photon sphere that surrounds it. We further present the complete 3D shadow, incorporating observer inclination and relativistic effects to provide a direct link to high-resolution interferometric imaging. In addition, we have determined the scalar field perturbation in the interior and computed its quasinormal modes using the third-order WKB approximation. The potential is plotted against the tortoise coordinate and shows a single peak with an asymptotic decay, as expected for a stable configuration. Our stability analysis, evidenced by imaginary negative quasinormal modes for various values of

$$\eta $$ η

, predicts detectable ring-down overtones for the LISA and the Einstein Telescope, thereby establishing a direct phenomenological link between our model and upcoming gravitational-wave observations.