Bound orbits around charged black strings

TL;DR

This paper investigates the geodesics of 5D charged black strings, revealing unique bound and null orbits, including stable null orbits outside horizons, which differ from 4D black hole behavior.

Contribution

It provides a comprehensive taxonomy of bound orbits around 5D charged black strings and compares their properties to 4D black holes, highlighting new stable null orbits.

Findings

High-energy particles can form bound orbits around black strings.

Radial periods have larger accumulated angles than in 4D.

Stable null orbits exist outside horizons in 5D, unlike in 4D.

Abstract

We study the geodesics of $5d$ Reissner-Nordstrom and nonsingular black strings, and establish a rational bound orbit taxonomy for both massive as well as null test particles. For the timelike case, test particles with high energy (that would have made them plunge into or scatter off a black hole) could still form bound orbits around the black strings. We calculate the accumulated angles of the corresponding radial periods and show that they are higher than their $4d$ counterparts. For the null case, we found the existence of stable null orbits outside their respective horizons, which do not exist in the four dimensions except at their extremal limit.