2005/12/31 by Avery E. Broderick, Ramesh Narayan · 2 citations
Engineering · Physics and Astronomy · #Astrophysical Phenomena and Observations #Heat Transfer Mechanisms #Pulsars and Gravitational Waves Research #astro-ph #gr-qc
paper · pdf · doi:10.1086/500930
published as Astrophys.J.638:L21-L24,2006 · 6 pages, 2 figures, submitted to ApJ Letters
openalex publication_date 2006/01/23 · arxiv created 2006/03/31 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We consider a model in which Sgr A*, the 3.7 × 10 6 M ☉ supermassive black hole candidate at the Galactic center, is a compact object with a thermally emitting surface. For very compact surfaces within the photon orbit, the thermal assumption is likely to be a good approximation because of the large number of rays that are strongly gravitationally lensed back onto the surface. Given the very low quiescent luminosity of Sgr A* in the near-infrared, the existence of a hard surface, even in the limit in which the radius approaches the horizon, places a severe constraint on the steady mass accretion rate onto the source: ≲ 10 -12 M ☉ yr -1 . This limit is well below the minimum accretion rate needed to power the observed submillimeter luminosity of Sgr A*: > 10 -10 M ☉ yr -1 . We thus argue that Sgr A* does not have a surface, i.e., that it must have an event horizon. The argument could be made more restrictive by an order of magnitude with microarcsecond resolution imaging, e.g., with submillimeter very long baseline interferometry.