{"work":{"id":"78d9552f-3b2d-4107-ab54-a1fb3f25caff","openalex_id":null,"doi":null,"arxiv_id":"gr-qc/0005050","raw_key":null,"title":"The geometry of photon surfaces","authors":null,"authors_text":"C","year":2000,"venue":"gr-qc","abstract":"The photon sphere concept in Schwarzschild space-time is generalized to a definition of a photon surface in an arbitrary space-time. A photon sphere is then defined as an SO(3)xR-invariant photon surface in a static spherically symmetric space-time. It is proved, subject to an energy condition, that a black hole in any such space-time must be surrounded by a photon sphere. Conversely, subject to an energy condition, any photon sphere must surround a black hole, a naked singularity or more than a certain amount of matter. A second order evolution equation is obtained for the area of an SO(3)-invariant photon surface in a general non-static spherically symmetric space-time. Many examples are provided.","external_url":"https://arxiv.org/abs/gr-qc/0005050","cited_by_count":null,"metadata_source":"pith","metadata_fetched_at":"2026-05-22T23:32:15.260072+00:00","pith_arxiv_id":"gr-qc/0005050","created_at":"2026-05-10T07:37:04.729944+00:00","updated_at":"2026-06-05T21:23:00.469572+00:00","title_quality_ok":false,"display_title":"The geometry of photon surfaces","render_title":"The geometry of photon surfaces"},"hub":{"state":{"work_id":"78d9552f-3b2d-4107-ab54-a1fb3f25caff","tier":"hub","tier_reason":"10+ Pith inbound or 1,000+ external citations","pith_inbound_count":10,"external_cited_by_count":null,"distinct_field_count":1,"first_pith_cited_at":"2025-03-27T06:45:23+00:00","last_pith_cited_at":"2026-05-09T12:16:37+00:00","author_build_status":"not_needed","summary_status":"needed","contexts_status":"needed","graph_status":"needed","ask_index_status":"not_needed","reader_status":"not_needed","recognition_status":"not_needed","updated_at":"2026-06-08T18:24:07.131841+00:00","tier_text":"hub"},"tier":"hub","role_counts":[{"context_role":"background","n":5},{"context_role":"method","n":1}],"polarity_counts":[{"context_polarity":"background","n":4},{"context_polarity":"unclear","n":1},{"context_polarity":"use_method","n":1}],"runs":{},"summary":{},"graph":{},"authors":[]}}