Black Hole shadows of $\alpha'$-corrected black holes

TL;DR

This paper investigates how string theory corrections, specifically $\alpha'$ corrections, affect the observable shadows of rotating black holes, revealing measurable deviations from classical Kerr black hole images.

Contribution

It provides a detailed analysis of $\alpha'$-corrected black hole shadows, including geometry, ISCO, photon ring, and image features, extending previous Kerr models.

Findings

$\alpha'$ corrections increase shadow diameter, displacement, and asymmetry.

Deviations from Kerr are maximized at different viewing angles.

The study offers potential observational signatures of string theory effects in black hole images.

Abstract

In this paper we study the qualitative features induces by corrections to GR coming from String Theory, on the shadows of rotating black holes. We deal with the slowly rotating black hole solutions up to order $\mathcal{O}(a^3)$, to first order in $\alpha'$, including also the dilaton. We provide a detailed characterization of the geometry, as well as the innermost stable circular orbit (ISCO) and photon ring, and then we proceed to obtain the black hole images within the relativistic thin-disk model. We characterize the images by computing the diameter, displacement and asymmetry. A comparison with the Kerr case, indicates that all these quantities grow due to the $\alpha'$ correction, and that the departure from GR for different observable is enhanced depending on the angle of view, namely for the diameter the maximum departure is obtained when the system is face-on, while for the displacement and asymmetry the departure from GR is maximized for edge-on point of view.