In 2019, the Event Horizon Telescope captured the first image of the supermassive black hole in the M87 galaxy. A few days ago, the “Sagittarius A* (Sgr A*)” supermassive black hole in the center of the Milky Way was photographed again.
Size comparison of the black hole at the center of the M87 galaxy (left) and the black hole at the center of the Milky Way (right)
The Event Horizon Telescope is not actually a “one” ground-based telescope, but uses the Ultra-Long Baseline Interferometry (VLBI) technology to connect a total of 8 radio telescopes (EHT) around the world to form a virtual intercontinental telescope with the size of the Earth. The resolution is about as large as a grain of sand can be seen from Hong Kong to Tokyo, Japan.
The black hole at the center of the Milky Way is 27,000 light-years away from Earth, so the research team observed Sgr A* over multiple nights, collecting data for several hours at a time. According to published data, the mass of this black hole has exceeded the mass of the sun by 4 million times. It only takes a few minutes for the gas to circle around, and because the image changes so quickly, it is quite difficult to focus and obtain a clear image.
So the research team needed to develop more sophisticated correction techniques and imaging methods to bring Sgr A* to our eyes. The team assembled more than 300 researchers from 80 institutes around the world, and after extensive simulations and adjustments, it took five years to complete the imaging. And it is reported that the image reconstruction of Sgr A* is more difficult than that of M87.