Null Geodesics and Strong Field Gravitational Lensing in a String Cloud Background

摘要

This paper is devoted to studying two interesting issues of a blackhole with string cloud background. Firstly, we investigate nullgeodesics and find unstable orbital motion of particles. Secondly,we calculate deflection angle in strong field limit. We then findpositions, magnifications, and observables of relativistic images forsupermassive black hole at the galactic center. We conclude thatstring parameter highly affects the lensing process and results turnout to be quite different from the Schwarzschild black hole.