Identifying doppelgange Black Holes through Shadow Images

TL;DR

This paper studies how doppelgänger black holes with identical radii but different charges produce distinct shadow images, revealing differences in optical appearance and shadow size despite similar horizons.

Contribution

It demonstrates that black holes with the same radius but different charges have distinguishable shadow images, especially under large magnetic charges, advancing black hole observational diagnostics.

Findings

Doppelgänger black holes have different shadow sizes despite identical radii.

Large magnetic charge black holes produce less clear bright rings inside shadows.

Shadow images can distinguish between black holes with the same horizon radius.

Abstract

Recently, an interesting \textit{doppelg\"ange} black hole solution is obtained in the string-inspired Euler-Heisenberg theory, where the black holes have the same radii but share different charges. We found, however, they possess different ISCOs and photon spheres, and hence affect their shadow images. In this work, we investigate the optical appearances, illuminated by an optically and geometrically thin disk, are investigated, of such black hole. One finds that doppelg\"ange black holes have different optical appearances. Even the horizon radii are the same, the size of shadows are not equal. Furthermore, we found that the large magnetic charge $Q_m$ black holes give rise to novel shadow images that the usual bright rings inside shadow are not clear, The optical appearances illuminated by spherically accretions are also examined, and it can also identify two doppelg\"ange black holes.