Strong Gravitational Lensing of Quasi-Kerr Compact Object with Arbitrary Quadrupole Moments

TL;DR

This paper investigates how arbitrary quadrupole moments in quasi-Kerr compact objects affect strong gravitational lensing, revealing potential observational differences from Kerr black holes that could help identify such objects.

Contribution

It introduces a model for quasi-Kerr objects with arbitrary quadrupole moments and analyzes their lensing properties, highlighting how these moments influence observable lensing features.

Findings

Photon-sphere radius varies with quadrupole correction parameter

Relativistic image positions are affected by quadrupole moments

Lensing coefficients differ from Kerr black holes depending on quadrupole parameter

Abstract

We study the strong gravitational lensing on the equatorial plane of a quasi-Kerr compact object with arbitrary quadrupole moments which can be used to model the super-massive central object of the galaxy. We find that, when the quadrupolar correction parameter $\xi$ takes the positive (negative) value, the photon-sphere radius $r_{ps}$, the minimum impact parameter $u_{ps}$, the coefficient $\bar{b}$, the relative magnitudes $r_m$ and the angular position of the relativistic images $\theta_{\infty}$ are larger (smaller) than the results obtained in the Kerr black hole, but the coefficient $\bar{a}$, the deflection angle $\alpha(\theta)$ and the angular separation $s$ are smaller (larger) than that in the Kerr black hole. These features may offer a way to probe special properties for some rotating compact objects by the astronomical instruments in the future.