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A vast international team of astronomers has captured the most intricate image yet of Sagittarius A* (SgrA*), the supermassive black hole at the center of the Milky Way. Taken using the Event Horizon Telescope, the image features brushstroke-like light shadows that offer hints about the black hole’s inner workings.
SgrA*—or our understanding of it—has come a long way since 1933, when an astronomer noticed a radio signal coming from the constellation Sagittarius. This constellation at the center of our galaxy gave the radio signal the moniker Sagittarius A. A few decades later, scientists at Virginia’s National Radio Astronomy Observatory found that Sagittarius A consisted of bright, compact subcomponents. They upgraded the object’s name to Sagittarius A* to honor their surprise and excitement about the radio source, utilizing the asterisk that typically denotes atomic “excitement.”
Further research eventually yielded two strange findings. Not only was SgrA* smaller than our solar system, but it was at least 4 million times more massive than our Sun. While these details would be at odds with each other under most circumstances, one reasonable explanation was left: SgrA* had to be a supermassive black hole.
Since then, several attempts have been made to measure and image SgrA*. One of the field’s most notable outcomes is the first-ever image of SgrA*, captured just three years after researchers grabbed the first direct image of Messier 87 (M87*). Both of these images were obtained using the Event Horizon Telescope, a network of radio observatories from all over the globe. Thanks to the same network, we now have an upgraded image of the supermassive black hole at the heart of our galaxy.
The first image of SgrA* released in 2022.
Credit: EHT Collaboration
Because black holes aren’t visible, scientists can only “see” one by interpreting light’s response to the hole’s gravitational field. Wednesday’s image is no different, but it does introduce a helpful twist. When researchers grabbed their first image of SgrA*, they noticed it looked a lot like M87*. This motivated them to compare the two.
While imaging M87* in polarized light in 2021 allowed astronomers to view the black hole in unprecedented detail, doing so with SgrA* would be much harder due to the latter black hole’s rapid movement and evolution. In a pair of papers published this week, a team of over 150 researchers worldwide explain how they circumvented these challenges and captured the above image.
The resulting snapshot reveals brushstroke-like magnetic fields swirling from the edge of SgrA*. These “strong and organized” fields suggest a magnetic structure similar to that of M87*, according to the team. This resemblance could mean there’s a jet hidden within SgrA*—a feature astronomers hope to find when they observe the supermassive black hole again in April 2024.
“The fact that the magnetic field structure of M87* is so similar to that of Sgr A* is significant because it suggests that the physical processes that govern how a black hole feeds and launches a jet might be universal among supermassive black holes, despite differences in mass, size, and surrounding environment,” Mariafelicia De Laurentis, deputy project scientist of the Event Horizon Telescope Collaboration, said. “This result allows us to refine our theoretical models and simulations, improving our understanding of how matter is influenced near the event horizon of a black hole.”