This paper is devoted to studying two interesting issues of a black hole with string cloud background. Firstly, we investigate null geodesics and find unstable orbital motion of particles. Secondly, we calculate deflection angle in strong field limit. We then find positions, magnifications, and observables of relativistic images for supermassive black hole at the galactic center. We conclude that string parameter highly affects the lensing process and results turn out to be quite different from the Schwarzschild black hole.
En este trabajo se simulan geodésicas nulas para la métrica de dipolo masivo de Bonnor, implementando un algoritmo simbólico-numérico en Sage y Python. Este programa es capaz, en principio, de visualizar en 3D las geodésicas de cualquier métrica. Estas geodésicas inician en un punto común, formando colectivamente un cono de rayos de luz, simulando una sección de ángulo sólido de una fuente puntual frente a un objeto masivo con campo magnético. Se consideran también rayos de luz paralelos, y se simuló su cambio de trayectoria debida a la curvatura del espacio-tiempo.
Abstract
A reply to the previous article commenting on non-geodesical propagation of electromagnetic fields on gravitational backgrounds and the eikonal limit are presented.
The gravitational bending of light in the framework of conformal gravity is considered where an exact solution for null geodesics in the Mannheim-Kazanas is obtained. The linear coefficient γ characteristic to conformal gravity is shown to contribute enhanced deflection compared to the angle predicted by General Relativity for small γ. We also briefly consider gravitational lensing in covariant emergent gravity.
Null geodesics and thermodynamic phase transition of four-dimensional Gauss–Bonnet AdS black hole