https://doi.org/10.1140/epjc/s10052-018-6160-y
Regular Article - Theoretical Physics
Lower bound on the radii of circular orbits in the extremal Kerr black-hole spacetime
1
The Ruppin Academic Center, 40250, Emeq Hefer, Israel
2
The Hadassah Academic College, 91010, Jerusalem, Israel
* e-mail: shaharhod@gmail.com
Received:
24
July
2018
Accepted:
16
August
2018
Published online:
7
September
2018
It is often stated in the physics literature that maximally-spinning Kerr black-hole spacetimes are characterized by near-horizon co-rotating circular geodesics of radius 
with the property 
, where 
is the horizon radius of the extremal black hole. Based on the famous Thorne hoop conjecture, in the present compact paper we provide evidence for the existence of a non-trivial lower bound 
on the radii of circular orbits in the extremal Kerr black-hole spacetime, where 
is the dimensionless mass ratio which characterizes the composed black-hole-orbiting-particle system.
© The Author(s), 2018
