Astronomers have finally solved an over 50-year mystery about the supermassive black hole at the center of our Milky Way galaxy.
Most black holes produce wind or jets as they eat surrounding materials. Until now, no one could find the wind produced by Sagittarius A*, the one controlling our galaxy’s growth and evolution.
But the most detailed view of the black hole yet has provided a much clearer view of what they say is 20,000-year-old wind, helping scientists better understand its role in the cosmos.
“Unless a black hole exists in a perfect vacuum, it must blow a wind somehow,” Mark Gorski, an astrophysicist at Northwestern University who co-led the study, explained in a statement. “And there is no perfect vacuum in the universe.”
“With new observations, this is the first time we’ve had a clean enough view to see the wind’s imprint. We looked at the data and said, ‘There it is. There is the thing that everybody’s been looking for for 50 years,’” he said.
The researchers used five years of observations from the Atacama Large Millimeter/Submillimeter Array radio telescopes in Chile, peering through gas and dust previously obscuring our view of Sagittarius A*.
Capturing an image of the gas near the black hole, the researchers then corrected it to reduce the black hole’s radio signals, which are emitted from matter around the black hole.
The image was 100 times deeper and 80 times sharper than previous maps of the region, allowing the scientists to see areas that were invisible in past photos.
That’s how they found a massive, cone-shaped hole without gas, which could only have been created by hot wind.
Winds produced by stars around the black hole are not powerful enough to carve out a region this size, they say.
“If you blow hot material from the black hole, it’s not going to want to exist with the cold material,” Gorski said. “It’s either going to push the cold material out or heat it up. And, if it’s too hot, you will no longer see the cold gas.”
“The wind is not powerful, and its direction probably wanders with time. It shows that our black hole is not unique, and our place in the universe is not unique,” Elena Murchikova, who co-led the study with Gorski, said.
The observations indicate the black hole is in a quieter phase. Although, there has been evidence of past disruptions, and NASA’s Chandra X-ray Observatory previously saw X-ray emissions in the same region as the cone-shaped hole.
Sagittarius A* was first discovered in 1974.
“Exceptional claims require exceptional evidence,” Gorski said. “We wanted to make sure that we weren’t just looking at some sort of imaging artifact. Then, the X-ray image from Chandra just slotted in perfectly. The molecular features lined up.”
“When you find something that no one has seen before, the first thought that runs through your mind is not ‘Oh my God, we made a discovery,’” Murchikova said. “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.”
