Year: 2026
Type: preprint
Abstract: Energy conditions (ECs) underpin fundamental results in general relativity, yet their observational validity in strong gravitational fields remains largely untested. Here, we establish a direct correspondence between the local stress-energy tensor, photon-orbit dynamics, and strong-field observables associated with black hole shadows, photon rings, and eikonal gravitational-wave ringdown for static, spherically symmetric black holes within general relativity. We show that imposing local ECs at unstable photon spheres yields analytic bounds on these observables. In particular, the demagnification of successive photon rings provides an exact diagnostic of the local tangential null energy condition. These bounds offer a direct route to constraining the matter fields sourcing spacetimes and testing ECs through strong-field observations. Combining them with observational measurements of these observables further restricts admissible black hole geometries and additionally constrains the otherwise inaccessible photon sphere geometry and local stress-energy content, demonstrating their observational potential in the strong-field regime.
Source: arXiv (Cornell University)
Institutions: University of Arizona, Netaji Subhas University of Technology
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Award: G1479333071
OpenAlex ID: W7168242020