2025/09/01 by Roberto Giambò, Giambò, Roberto, Camilla Lucamarini +1 · 1 voice
Physics and Astronomy · #Black Holes and Theoretical Physics #Cosmology and Gravitation Theories #FOS: Physical sciences #General Relativity and Quantum Cosmology (gr-qc) #Pulsars and Gravitational Waves Research #gr-qc
paper · pdf · doi:10.48550/arxiv.2509.01368
openalex publication_date 2025/09/01 · arxiv published 2025/09/01 · openalex created_date 2025/10/10 · arxiv updated 2026/03/05 · openalex updated_date 2026/07/28
The equations for the photon surface in spherical symmetry are worked out, starting from arXiv:gr-qc/0005050, in the most general dynamical setting. We show that the condition for a timelike hypersurface to be a photon surface can be reformulated as a non-autonomous dynamical system, whose analysis reveals that the same condition also holds when the surface is generated by a null radial geodesic. As an application, we consider a well-known model of a spherical dust cloud undergoing gravitational collapse. Comparing our findings with those in arXiv:1910.13758 we establish that the photon surface uniquely extends in the interior spacetime as a null hypersurface, allowing us to analytically investigate whether it covers the singularity developing in the LTB model.