The Milky Way's black hole may have formed this curious tunnel in space
Suddenly, the Milky Way's central black hole is starting to look a little less like a weirdo.
Astronomers have discovered a large cone-shaped void in gas surrounding Sagittarius A*, the galaxy's supermassive black hole, that could solve a longstanding mystery.
All active black holes should blow winds or jets of material back into space while they're feeding, according to theory. That process is how supermassive black holes shape the galaxies around them. But no matter how hard astronomers have looked, they haven't seen our black hole, dubbed Sgr A* for short, pushing anything back out.
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New images from a Northwestern University-led research team now suggest this cone tunneling through a fog of cold gas is evidence of that missing wind. It was almost literally an arrow pointing back at the black hole, said Mark Gorski, who co-led the study.
"This is the first time we've had a clean enough view to see the wind's imprint," Gorski said in a statement. "We looked at the data and said, 'There it is. There is the thing that everybody's been looking for for 50 years.'"
In reality, the discovery wasn't that straightforward of an a-ha moment. Only after the team had overlaid their picture with data from NASA's Chandra X-ray Observatory did their observations begin to make sense. That gave them confidence the odd cone wasn't just an imaging artifact, they said.
"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,'" said coauthor Elena Murchikova, in a statement. "It's 'Oh my God, what's wrong with my analysis?'"
Scientists believe virtually all large galaxies have a supermassive black hole at their core. These are regions millions to billions of times more massive than the sun. In fact, so much mass is packed into these small spaces that gravity becomes strong enough to prevent anything from escaping — even light.
These black holes don't just sit around, waiting for gas, dust, and stars to fall in, but they influence how their galaxies evolve around them by sucking in material and also blowing material that comes near their boundary — called the event horizon — back out.
By taking high-resolution observations with Atacama Large Millimeter/Submillimeter Array in Chile over about five years, the team was able to map cold gas near the black hole in unprecedented detail. This ALMA image is 100 times deeper and 80 times sharper than previous maps, according to the researchers.
The cone stretches one to three light-years away from the black hole. The simplest explanation after careful consideration, according to the team's findings published in The Astrophysical Journal Letters, is that a fast, energetic stream of hot material has launched out of the black hole's region, shoving colder gas in its path out of the way.
The team determined it would take more energy than could be provided by all the stars in that area to create the conic gap. The researchers estimated the wind has probably been blowing for 20,000 years or more.
Based on the image, the direction of Sgr A*'s wind seems somewhat tilted and uneven, which suggests it may be weak and mangled by surrounding gas as it travels.
How this feature has escaped the notice of previous researchers is not too surprising, the researchers said. In order to see into our own galaxy's center, astronomers have to look through the plane of the Milky Way, which is thick with gas, dust, and ionized structures. Sgr A* may also be in a quieter lull, making the distant activity harder to spot.
Some scientists have previously suggested that the lack of wind or jets could mean Sgr A* is an exotic black hole — an outlier among hundreds of billions of others like it. If anything, Murchikova is now convinced of the opposite.
"It shows that our black hole is not unique, and our place in the universe is not unique," she said.
Topics NASA
Elisha Sauers writes about space for Mashable, taking deep dives into NASA's moon and Mars missions, chatting up astronauts and history-making discoverers, and jetting above the clouds. Through 17 years of reporting, she's covered a variety of topics, including health, business, and government, with a penchant for public records requests. She previously worked for The Virginian-Pilot in Norfolk, Virginia, and The Capital in Annapolis, Maryland. Her work has earned numerous state awards, including the Virginia Press Association's top honor, Best in Show, and national recognition for narrative storytelling. For each year she has covered space, Sauers has won National Headliner Awards, including first place for her Sex in Space series. Send space tips and story ideas to [email protected] or text 443-684-2489. Follow her on X at @elishasauers.
