2019/01/18 by Sara Issaoun, S. Issaoun, M. D. Johnson +73 · 8 citations
Physics and Astronomy · #Accretion (finance) #Active galactic nucleus #Angular diameter #Angular resolution (graph drawing) #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Event (particle physics) #Event horizon #Galactic Center #Galaxy #Interstellar medium #Millimeter #Optics #Physics #Radio Astronomy Observations and Technology #Sagittarius A* #Scattering #Schwarzschild radius #Star formation #Stars #Submillimeter Array #Supermassive black hole #Very Long Baseline Array #Very-long-baseline interferometry #astro-ph.HE
paper · pdf · doi:10.3847/1538-4357/aaf732
Accepted for publication in ApJ
arxiv created 2019/01/18 · openalex publication_date 2019/01/20 · arxiv updated 2019/01/21 · openalex created_date 2020/11/23 · openalex updated_date 2026/08/06
Abstract The Galactic center supermassive black hole Sagittarius A* (Sgr A*) is one of the most promising targets to study the dynamics of black hole accretion and outflow via direct imaging with very long baseline interferometry (VLBI). At 3.5 mm (86 GHz), the emission from Sgr A* is resolvable with the Global Millimeter VLBI Array (GMVA). We present the first observations of Sgr A* with the phased Atacama Large Millimeter/submillimeter Array (ALMA) joining the GMVA. Our observations achieve an angular resolution of ∼87 μ as, improving upon previous experiments by a factor of two. We reconstruct a first image of the unscattered source structure of Sgr A* at 3.5 mm, mitigating the effects of interstellar scattering. The unscattered source has a major-axis size of 120 ± 34 μ as (12 ± 3.4 Schwarzschild radii) and a symmetrical morphology (axial ratio of ), which is further supported by closure phases consistent with zero within 3 σ . We show that multiple disk-dominated models of Sgr A* match our observational constraints, while the two jet-dominated models considered are constrained to small viewing angles. Our long-baseline detections to ALMA also provide new constraints on the scattering of Sgr A*, and we show that refractive scattering effects are likely to be weak for images of Sgr A* at 1.3 mm with the Event Horizon Telescope. Our results provide the most stringent constraints to date for the intrinsic morphology and refractive scattering of Sgr A*, demonstrating the exceptional contribution of ALMA to millimeter VLBI.