On May 18th, from 18:30-21:00 (Beijing time), the 13th Tsung-Dao Lee frontier lecture was held online with the title of “First Sgr A* Event Horizon Telescope Results: The Shadow of the Supermassive Black Hole in the Center of the Milky Way” . Following the lecture, a colloquium on this topic was also given by the same speaker, Dr. Yosuke Mizuno, Tsung-Dao Lee Fellow, a member of the EHT collaboration. Prof. Pengjie Zhang from the School of Physics and Astronomy and the deputy director of the Astronomy & Astrophysics Division of Tsung-Dao Lee Institute (TDLI) hosted the lecture and colloquium. In addition, Prof. Zhiqiang Shen, the director of Shanghai Astronomical Observatory, Prof. Xiaogang He from TDLI and Dr. Yuzhu Cui from TDLI have been invited to attend the panel discussion. Around 1800 audiences has joined these activities online.
At 9pm, May 12th Beijing time, the Event Horizon Telescope (EHT) collaboration released the first Sgr A* results simultaneously at 7 different places around the world. This is another breakthrough made by EHT collaboration following their 2019 release of the first image of a black hole, called M87*, at the center of the more distant galaxy Messier 87.
Yosuke Mizuno, as the Theory & Simulation Working Group Coordinator in EHT, is in charge of the development of the database of black hole simulations. At the beginning of the frontier lecture, he firstly introduced EHT collaboration which has already more than 300 members from 5 continents, devoting themselves to capture the first images of the black holes with the technique of Very Long Baseline Interferometry (VLBI) at submillimeter wavelengths.
Then he systematically reviewed the black holes’ research history, fundamental properties, and compared the differences between rotating black holes and non-rotating black holes. Such as, a black hole is the densest object in the universe, its gravity pulls so much that even light can not get out. The black hole theory originates from a solution of the general relativity equation, and the “no-hair” theorem indicates that the black holes are characterized only by their mass, angular momentum and electrical charge. Following the detailed introduction of the background knowledge, Yosuke Mizuno presented the latest research results of Sgr A*, and the whole process of producing the results, and what can we learn from these results.
At the end of the lecture, Yosuke Mizuno visioned EHT’s future plans, and summarized his talk, including that Sgr A* has a bright “donut” structure; the images of Sgr A* can be clustered into four groups based on similar features, three of the clusters show a ring structure but, with differently distributed brightness around the ring; the ring diameter of Sgr A* is 52 micro-arcseconds (μas), and its existing is consistent with the expected appearance of a Kerr black hole with mass ~ 4 × 106 solar masses; these results provide first direct visual evidence of existing supermassive black hole at the center of our Milk Way; furthermore, a comparison with M87*, in spite of spanning over three orders of magnitude in central mass, both of their observational results agreed with predictions from Einstein’s Theory of General Relativity.
At the panel discussion, Zhiqiang Shen, Pengjie Zhang, Xiaogang He, Yuzhu Cui and Yosuke Mizuno shared their opinions and knowledge on the results, and called for further collaboration and exchange with each other, and they welcomed and encouraged more young scientists to join the research work on black holes and wished EHT obtain more groundbreaking discoveries in the future.
In the colloquium, Yosuke Mizuno presented more details on the Sgr A* results from the views of theoretical explanation and modeling comparisons, described the accretion properties near Sgr A*.
Video Link：https://vshare.sjtu.edu.cn/open/2c03a6335894aba9600be485250262cb