Astronomers have finally solved a decades-old mystery about the supermassive black hole at the centre of our galaxy, Sagittarius A*. For over 50 years, scientists have searched for the wind produced by this black hole, which controls the Milky Way's growth and evolution. Now, using the most detailed view yet, they have identified a 20,000-year-old wind, shedding light on the black hole's role in the cosmos.
“Unless a black hole exists in a perfect vacuum, it must blow a wind somehow,” said Mark Gorski, an astrophysicist at Northwestern University who co-led the study. “And there is no perfect vacuum in the universe.” The team used five years of observations from the Atacama Large Millimeter/Submillimeter Array (ALMA) radio telescopes in Chile, peering through gas and dust that had previously obscured the view.
By capturing an image of the gas near the black hole and correcting it to reduce radio signals, the researchers produced a map 100 times deeper and 80 times sharper than previous ones. This revealed a massive, cone-shaped hole without gas, carved out by hot wind. Winds from surrounding stars were not powerful enough to create such a feature.
“If you blow hot material from the black hole, it's not going to want to exist with the cold material,” Gorski explained. “It's either going to push the cold material out or heat it up.” The wind is not powerful and its direction likely wanders over time, suggesting our black hole is not unique. “Our place in the universe is not unique,” added co-lead Elena Murchikova.
The observations indicate Sagittarius A* is in a quieter phase, though past disruptions have been noted. X-ray data from NASA's Chandra Observatory aligned perfectly with the cone-shaped hole, confirming the finding. “Exceptional claims require exceptional evidence,” Gorski said. “When you find something that no one has seen before, the first thought is not 'Oh my God, we made a discovery,'” Murchikova added. “It's 'Oh my God, what's wrong with my analysis?' But when we overlaid our image with the X-ray image, it started to make sense.”
