Milky Way shows faint black hole wind near Sagittarius A*

cone-shaped void – New Milky Way observations of Sagittarius A* reveal a cone-shaped cavity in cold carbon monoxide close to the black hole—evidence that even a quiet supermassive black hole can drive a mild, hot wind.

For decades, astronomers have hunted for something elusive at the Milky Way’s core: not a violent blast, but a gentle exhale.

Now, after what the field has described as 50 years of searching, evidence has emerged for a mild wind blowing from Sagittarius A*, the supermassive black hole at the center of our galaxy. The new findings were reported June 4 in Astrophysical Journal Letters.

“We’ve never seen gentle breezes from black holes, but likely that’s what they do most of their lives,” says astrophysicist Lena Murchikova of Northwestern University in Evanston, Ill. “Now, for the first time, we see this gentle breeze from the black hole.”

The story starts with how black holes interact with their surroundings. As black holes consume gas and dust, the material around them heats up. That heat emits radiation that pushes away gas and other material, creating wind. When a black hole is eating heavily. those winds can be powerful enough to send material clear out of the galaxy. But when a black hole is eating minimally and is in a quiet state—like Sagittarius A*—astronomers have expected the wind to be lighter.

Finding proof of any such “breezy” wind has been hard for a simple reason: the galactic center is obscured. Gas, stars and dust shroud the view, making it difficult to see what’s happening close to the black hole.

Astronomers also only got their target in the first place decades ago. Sagittarius A* was discovered in the 1970s, when astronomers were just starting to consider that the unidentified object could be a supermassive black hole. Since then, the theorized wind has remained largely out of reach.

Some hints turned up at a distance. In the past 15 years. X-ray and gamma-ray evidence for wind was found far from the black hole—at times even extending outside the galaxy. That suggested episodes of strong gales in the past. But with no confirmation near Sagittarius A*. researchers couldn’t be sure whether the black hole was still breezy now. or if those winds belonged to an older. more turbulent era.

In the new study. Murchikova and astronomer Mark Gorski. also at Northwestern. gathered more than 100 hours of observations of Sagittarius A*. The data were taken over five years with the Atacama Large Millimeter/Submillimeter Array radio telescopes in Chile. Those observations revealed the distribution of cold carbon monoxide. described as a key indicator of gas. up close to Sagittarius A*.

To extract more from that faint view, the team used a new way to process the data. With it, they could see gas, dust and other materials 100 times fainter than what could be seen before, and they produced an image of the black hole’s neighborhood 80 times sharper than earlier attempts.

What they saw was a sharp. telltale feature: a cone-shaped gap by the black hole that. unlike the surrounding region. is devoid of cold carbon monoxide. The researchers say the geometry of this void—and previous observations of X-rays showing hot gas in the same region—points to the same culprit: hot wind flowing out from Sagittarius A*.

The picture is stark: a cone-shaped cavity near the Milky Way’s central black hole suggests hot winds there are blowing away colder gas.

“Supermassive black holes throughout the universe live most of their time in a quiet state,” Gorski says. “So [these findings] tell us that even though most black holes are pretty quiet, they’re still having an impact.”

The implications reach beyond one odd feature in a complicated galaxy. Winds from black holes can slow star formation and limit the food available to a growing black hole. They can also help trigger star formation by compressing clouds of dust. Understanding wind from a quiet black hole like Sagittarius A* could therefore help explain how black holes sculpt their galaxies even when they appear relatively calm.

Still, the evidence is not the final word. Rebecca Diesing. an astrophysicist at Columbia University who was not involved in the research. called the potential discovery “indeed a big deal. ” saying it would show that our supermassive black hole is not unique and produces a wind much like those in other galaxies.

But Diesing said she wants more than an absence of gas. Future observations could confirm the wind by probing the velocity of gas being swept out of the cavity. She also pointed to a longer-term test: it may even be possible to see the edges of the void wobble over time as the wind keeps on blowing.

For now, the quiet black hole at the heart of the Milky Way has left a footprint—one cone-shaped gap in cold carbon monoxide that, researchers say, only a hot wind could carve.

Sagittarius A* black hole winds cold carbon monoxide ALMA hot gas Astrophysical Journal Letters Milky Way galactic center