Remarks on the black hole shadows in Kerr-de Sitter space times

This work is geared towards analysis of shadows cast by Kerr-de Sitter (KdS) and Kerr-de Sitter Revisited (RKdS) black holes. Considering observers in the vicinity of the static radius, we derive the impact parameters defining the apparent positions of the shadows. Such observers are of interest to our work because embedding diagrams have shown that de Sitter space-time is analogous to an asymptotically flat one in the vicinity of the static radius. We also perform a comparative analysis between our result with that in Ref. [1]. Furthermore, we numerically obtain the radii of curvature, vertical diameters and horizontal diameters of the shadows. We find that for Lambda = 1.11 x 10(-52) m(-2), M87* observations cannot distinguish a RKdS black hole shadow from that of a Kerr black hole. Additionally, for the same value of Lambda, KdS and RKdS black hole shadows are, in practise, indistinguishable. Previously, it has also been shown that when Lambda = 1.11 x 10(-52) m(-2), KdS and Kerr black hole shadows are indistinguishable. Utilizing the 2017 EHT observations of M87* on the allowed range of the characteristic radius of the shadow, we obtain constraints on both black holes. When, a/M > 0.812311, we observe that large angles of inclination (theta > 30.5107 degrees) do not pass the constraints for both KdS and RKdS black holes.

Automated summary

This work focuses on analyzing the shadows generated by Kerr-de Sitter and Kerr-de Sitter Revisited black holes and derives the positions and parameters of the shadows for observers. It compares the results with previous studies and numerically obtains the curvature radii, vertical diameters, and horizontal diameters of the shadows. The findings suggest that under certain conditions, the shadows of these black holes are indistinguishable.