Photon spheres in dynamical spacetimes
Abstract
The characterization of the photon region -- i.e. the region of space-time filled with unstable bound null geodesics -- is critical to understand the behavior of radiation near a compact-enough object, such as black holes. However, its study has been typically focused on stationary space-times that leave outside interesting theoretical and phenomenological scenarios such as collapsing, accreting, or evaporating black holes, besides time-dependent configurations such as those found in some boson star models. In this work, we present a novel covariant approach to describe radiation in dynamical spherical space-times. This allows a general description of photon surfaces and their dynamics in non-static space-times, recovering well known expressions in the static limit and clarifying their meanings. Furthermore, we illustrate our results via several examples of dynamical scenarios in stellar collapse and accreting/evaporating models, and discuss the open caveats regarding such scenarios.
Versions
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BibTeX
@misc{diazguerra2026photon,
title = {{Photon spheres in dynamical spacetimes}},
author = {David Díaz-Guerra and Ángel Rincón and Diego Rubiera-Garcia},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.01916},
eprint = {2606.01916},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.01916},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Photon spheres in dynamical spacetimes
AU - David Díaz-Guerra
AU - Ángel Rincón
AU - Diego Rubiera-Garcia
PY - 2026
DA - 2026/10/22
PB - arXiv
DO - 10.48550/arxiv.2606.01916
UR - https://arxiv.org/abs/2606.01916
AB - The characterization of the photon region -- i.e. the region of space-time filled with unstable bound null geodesics -- is critical to understand the behavior of radiation near a compact-enough object, such as black holes. However, its study has been typically focused on stationary space-times that leave outside interesting theoretical and phenomenological scenarios such as collapsing, accreting, or evaporating black holes, besides time-dependent configurations such as those found in some boson star models. In this work, we present a novel covariant approach to describe radiation in dynamical spherical space-times. This allows a general description of photon surfaces and their dynamics in non-static space-times, recovering well known expressions in the static limit and clarifying their meanings. Furthermore, we illustrate our results via several examples of dynamical scenarios in stellar collapse and accreting/evaporating models, and discuss the open caveats regarding such scenarios.
ER -