This time, it’s done. After years of effort, the teams of the Event Horizon Telescope succeeded in drawing the portrait of “our” black hole, the one which is in the center of the Milky Way. The announcement was made this afternoon during a series of press conferences held simultaneously in several countries.
It is not directly the black hole which is observed — since nothing can escape from it — but rather its shadow on the background of superheated and luminous gas which is attracted towards it by its considerable mass. This makes it possible to determine what is called the event horizon of this invisible star: below this limit, everything that penetrates — matter or light — is swallowed up and disappears from our eyes.
To achieve this feat, the scientists combined the images of 43 radio telescopes of a few meters – the largest displays 30 m in diameter – installed in the United States, Hawaii, Mexico, Chile, Spain, France, as well as in Greenland and Antarctica. This amounts to simulating a virtual instrument more than 10,000 kilometers wide and thus increasing the resolution considerably.
Located 26,000 light-years from us, Sagittarius A* weighs about 4 million solar masses. German Reinhard Genzel and American Andrea Ghez received half of the 2020 Nobel Prize in Physics for discovering its existence in the 1990s, with Britain’s Roger Penrose receiving the other half for demonstrating the process of hole formation black, based on the theory of general relativity.
In April 2019, the EHT collaboration presented the first image of a supermassive black hole, located in the constellation of Virgo, at the center of the Messier 87 galaxy, 50 million light-years from us. Called M87*, it is a real giant since it weighs the equivalent of 6.5 billion times our sun. At the time, attempts to make the same observation on Sagittarius A* had failed.