Seth Fletcher in Scientific American:
The mystery at the heart of the Milky Way has finally been solved. This morning, at simultaneous press conferences around the world, the astronomers of the Event Horizon Telescope (EHT) revealed the first image of Sagittarius A*, the supermassive black hole at the center of the Milky Way. It’s not the first picture of a black hole this collaboration has given us—that was the iconic image of M87*, which they revealed on April 10, 2019. But it’s the one they wanted most. Sagittarius A* is our own private supermassive black hole, the still point around which our galaxy revolves.
Scientists have long thought that a supermassive black hole hidden deep in the chaotic central region of our galaxy was the only possible explanation for the bizarre things that happen there—such as giant stars slingshotting around an invisible something in space at an appreciable fraction of the speed of light. Yet they’ve been hesitant to say that outright. For example, when astronomers Reinhard Genzel and Andrea Ghez shared a portion of the 2020 Nobel Prize in Physics for their work on Sagittarius A*, their citation specified that they were awarded for “the discovery of a supermassive compact object at the centre of our galaxy,” not the revelation of a “black hole.” The time for that sort of caution has expired.