Strong Lensing and Quasinormal modes of black hole around global monopole

TL;DR

This paper studies the effects of a global monopole on black hole properties, including gravitational lensing, shadow size, geodesic stability, and quasinormal modes, revealing how monopole parameters influence observable phenomena.

Contribution

It provides a comprehensive analysis of how global monopole parameters affect black hole lensing, shadow, geodesic stability, and electromagnetic quasinormal modes, which is novel.

Findings

Larger monopole parameters increase deflection angles and shadow radii.

The ISCO radius increases monotonically with the monopole parameter η.

Higher η results in slower damping of electromagnetic quasinormal modes.

Abstract

In this paper, we investigate various key aspects of a static and spherically symmetric black hole with global monopole. Firstly, we analyze the deflection angle in the strong field limit of massive particle by the global monopole. It shows that the angle of deflection increases when the two characteristic parameters for monopole configuration increase. The influence of the global monopole parameter on the lensing observables and the black hole shadow are studied. This shows that larger monopole parameter corresponds to larger shadow radii. The dynamics of timelike geodesics is also investigated in the spacetime. General circular orbits and the innermost stable circular orbits (ISCO) of timelike particles are discussed, highlighting that the monopole parameter significantly affects the circular orbits and the ISCO. In particular, it is observed that the radius of ISCO rises monotonically with $\eta$. In addition, the Lyapunov exponent is used to analyze the stability of timelike geodesics. The quasinormal modes for electromagnetic perturbation of the black hole with varying $\eta$ is also investigated. Our findings indicate that increasing the monopole parameter gives rise to gravitational waves with slower damping oscillations. To further validate the derived quasinormal mode spectrum, we discuss the evolution of electromagnetic perturbations in the time domain profile, confirming the presence of the characteristic quasinormal ringing followed by late-time power-law tails.