Imaging of the Supermassive Black Hole in Our Galaxy, Sgr A* with the Event Horizon Telescope

【 2022年7月6日（水） → 2022年7月20日（水）に変更になリました。】

KOFUJI Yutaro（小藤 由太郎）
Department of Astronomy, School of Science, the University of Tokyo/National Astronomical Observatory of Japan（NAOJ）

The first event horizon scale image of the supermassive black hole in our Galaxy, Sgr A* was captured by the Event Horizon Telescope(EHT) Collaboration. EHT is the Very Long Baseline Interferometry (VLBI) that links radio dishes around the world to create an Earth-sized telescope virtually. High-resolution observations of EHT enable us to see the vicinity of the black hole. The obtained image of the black hole shadow is consistent with the prediction of general relativity.
The observations were done in 2017 April at a wavelength of 1.3mm. In the imaging process, we used 4 imaging methods, CLEAN, regularized maximum likelihood (RML) methods, and a Bayesian posterior sampling method. The main challenges of Sgr A* imaging are the rapid time variation and interstellar scattering, and the mitigation processes for these effects are developed. Each imaging method has imaging parameters including these mitigation processes and we performed the parameter survey using ~200 thousand parameter combinations. From these parameters, we choose ~10 thousand "Top Set" parameters that can distinguish different morphologies. The Sgr A* images reconstructed with "Top Set" parameters are clustered into 4 morphologies, 3 ring clusters that have different brightness distributions and a small number of non-ring images. Based on the multiple tests, we conclude that Sgr A* is highly likely to have ~50 micro-arcsecond ring structure. The comparison between the reconstructed images and the theoretical simulations shows that reconstructed images are consistent with the shadow of the Kerr black hole which weighs ~4 million solar masses.

A 2F Conf. room（1236） / 研究管理棟２階会議場（1236号室）、Via Zoom / Zoom 開催