The length of a compact extra dimension from black hole shadow

TL;DR

This paper uses black hole shadow observations to constrain the size of extra dimensions, providing evidence that such dimensions are compact and smaller than the Gregory-Laflamme instability threshold.

Contribution

It introduces a novel method to limit the size of compact extra dimensions using observational data from black hole shadows.

Findings

Rules out infinite extra dimension for black strings based on EHT data.

Constrains the compact extra dimension length to be smaller than the GL instability threshold.

Supports the hypothesis that extra dimensions are compact to avoid instability.

Abstract

Plenty of efforts have been made to explore the black string and its instability, but the fate of the black strings with fewer extra dimensions is still inconclusive. Now starting from the 5D uniform black string, we show that the EHT observations of M87* and SgrA* can not only rule out the black string with an infinite extra dimension, but also constrain the length of a compact extra dimension, which is much smaller than the critical length given from the Gregory-Laflamme (GL) instability. Our findings support the hypothesis that the extra dimension is compact avoiding the GL instability.