Strong gravitational lensing by rotating Simpson-Visser black holes

Abstract

We investigate strong field gravitational lensing by rotating Simpson-Visser black hole, which has an additional parameter (0 ≤ l/2M ≤ 1), apart from mass (M ) and rotation parameter (a). A rotating Simpson-Visser metric correspond to (i) a Schwarzschild metric for l/2M = a/2M = 0 and M = 0, (ii) a Kerr metric for l/2M = 0, |a/2M | < 0.5 and M = 0 (iii) a rotating regular black hole metric for |a/2M | < 0.5, M = 0 and l/2M in the range 0 < l/2M < 0.5 + (0.5) 2 − (a/2M ) 2 , and (iv) a traversable wormhole for a |a/2M | > 0.5 and l/2M = 0. We find a decrease in the deflection angle α D and also in the ratio of the flux of the first image and all other images r mag . On the other hand, angular position θ 1 increases more slowly and photon sphere radius x m decreases more quickly, but angular separation s increases more rapidly, and their behaviour is similar to that of the Kerr black hole. The formalism is applied to discuss the astrophysical consequences in the supermassive black holes NGC 4649, NGC 1332, Sgr A* and M87* and find that the rotating Simpson-Visser black holes can be quantitatively distinguished from the Kerr black hole via gravitational lensing effects. We find that the deviation of the lensing observables ∆θ 1 and ∆s of rotating Simpson Visser black holes from Kerr black hole for 0 < l/2M < 0.6 (a/2M = 0.45), for supermassive black holes Sgr A* and M87, respectively, are in the range 0.0422-0.11658 µas and 0.031709-0.08758 µas while |∆r mag | is in the range 0.2037-0.95668. It is difficult to distinguish the two black holes because the departure are in O(µas), which are unlikely to get resolved by the current EHT observations, and one has to wait for future observations by ngEHT can pin down the exact constraint. We also derive a two-dimensional lens equation and formula for deflection angle in the strong field limit by focusing on trajectories close to the equatorial plane.

On black bounces, wormholes and partly phantom scalar fields

“…The rich and diverse geometries obtained in this way have attracted much interest, and their extensions with rotation were also studied [20][21][22]. Further relevant studies concerned gravitational wave echoes at possible black hole/wormhole transitions, quasinormal modes of such space-times and gravitational lensing phenomena [23][24][25][26][27][28][29][30][31][32][33].…”

Scalar perturbations around rotating regular black holes and wormholes: quasi-normal modes, ergoregion instability and superradiance

“…Indeed, this class of compact objects interpolates smoothly between regular black holes and traversable wormholes, depending on the choice of the spin and this regularizing parameter. For all these reasons, Kerr-black-bounce solutions recently received considerable attention [44][45][46][47][48][49] and we here contribute to the study of their phenomenology by investigating the dynamics of a scalar test field propagating on top of the Kerr-black-bounce background. Specifically, we consider a massless scalar field and compute the QNMs; when the background is a traversable wormhole, we further search for unstable modes and derive the ensuing instability timescale.…”

Constraining a modified gravity theory in strong gravitational lensing and black hole shadow observations

“…Combing the expressions of deflection angle (26) and the lensing angle (30), we can evaluate the three observables of relativistic images, i.e. the angular position of the asymptotic relativistic images (θ ∞ ), angular separation between the outermost and asymptotic relativistic images (s), and relative magnification of the outermost relativistic image compared with other relativistic images (r mag ), as [9,74] (10) .…”