2013/10/24 by Shahar Hod · 6 citations
Physics and Astronomy · #Advanced Differential Geometry Research #Black Holes and Theoretical Physics #Black hole (networking) #Charged black hole #Classical mechanics #Cosmology and Gravitation Theories #Extremal black hole #General relativity #Gravitational collapse #Massless particle #Mathematical physics #Null (SQL) #Physics #Quantum mechanics #RADIUS #Rotating black hole #Schwarzschild radius #Spacetime #White hole #astro-ph.HE #de Sitter–Schwarzschild metric #gr-qc #hep-th
paper · pdf · doi:10.1016/j.physletb.2013.10.047
published as Physics Letters B 727, 345 (2013) · 10 pages
openalex publication_date 2013/10/24 · arxiv created 2017/01/23 · arxiv updated 2017/02/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
One of the most remarkable predictions of the general theory of relativity is the existence of black-hole “photonspheres”, compact null hypersurfaces on which massless particles can orbit the central black hole. We prove that every spherically-symmetric asymptotically flat black-hole spacetime is characterized by a photonsphere whose radius is bounded from above by rγ⩽3M, where M is the total ADM mass of the black-hole spacetime. It is shown that hairy black-hole configurations conform to this upper bound. In particular, the null circular geodesic of the (bald) Schwarzschild black-hole spacetime saturates the bound.