In various press conferences, representatives of the institutions collaborating in the Event Horizon Telescope (EHT) project announced that they obtained the first image of the area around Sagittarius A*, the supermassive black hole at the center of the Milky Way. The central shadow, which constitutes the black hole, is surrounded by a sort of ring formed by gas and dust that glow because they were heated by Sagittarius A*. It took the combination of 8 radio telescopes to obtain proof of the existence of this supermassive black hole, taken for granted by the vast majority of scientists but still denied by some.
The sensational results of the Event Horizon Telescope (EHT) project released on April 10, 2019, were just the first. On that occasion, they chose to focus on the area around the supermassive black hole of the galaxy Virgo A, also known as M87. The studies concerning M87 with the analyzes of the collected data offered more results published over time. However, the observation campaigns had already begun to detect emissions from the supermassive black hole at the center of the Milky Way, known as Sagittarius A*. At last, these results have arrived as well!
The appearance of Sagittarius A* with its ring is very similar to that of the area around the supermassive black hole of the galaxy M87. However, Sagittarius A* is small by comparison with a mass that is “only” a little over four million times the Sun’s. In fact, the supermassive black hole at the center of M87 is over a thousand times more massive, really huge even for the standards of these extreme objects.
The difference in size made it easier to generate the image released in 2019. Specifically, the problem is that the gas around Sagittarius A* takes a few minutes to orbit it against the many days it takes in the center of the galaxy M87. A more stable target is easier to observe and for this reason, it became the subject of the first images that were published. It took years of the work of over 300 researchers from 80 institutions of various nations to finally obtain this new result within the EHT project.
Having a second subject of study is important to further examine supermassive black holes and test our physical models, for example trying to understand the limits of the theory of relativity. The observation campaigns continued, as did the processing of the collected data. This means that we can expect further progress for Sagittarius A* as well with more detailed images and improvements in our models.