Fifty-year search ends
Astronomers have found evidence of a wind flowing from Sagittarius A*, the supermassive black hole at the center of our galaxy. The discovery, published in the Astrophysical Journal Letters, ends a five-decade search for direct proof that even quiet black holes can blow gas away from their surroundings.
Researchers Lena Murchikova and Mark Gorski of Northwestern University used more than 100 hours of observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, collected over five years. They analyzed cold carbon monoxide gas as a tracer near the black hole. A new data processing technique allowed them to detect material 100 times fainter than before, producing an image 80 times sharper of the black hole's neighborhood.
Cone-shaped void reveals the wind
The team spotted a cone-shaped gap in the cold gas extending from Sagittarius A*. Combined with earlier X-ray observations showing hot gas in the same region, the geometry points to a hot wind blowing outward from the black hole. "We've never seen gentle breezes from black holes, but likely that's what they do most of their lives," Murchikova said.
Sagittarius A* is currently in a quiet state, feeding minimally on nearby gas and dust. The wind is therefore mild compared to the powerful outflows seen from actively feeding black holes in other galaxies. Even so, it is enough to push away material that would otherwise form stars or fall into the black hole itself.
Black holes shape their galaxies
The finding helps explain how supermassive black holes influence their host galaxies even when dormant. By clearing nearby gas, the wind slows star formation and limits the black hole's own food supply. In some cases, the wind can also compress dust clouds and trigger new star formation.
"Supermassive black holes throughout the universe live most of their time in a quiet state. So these findings tell us that even though most black holes are pretty quiet, they're still having an impact," Gorski said. Future observations will look for velocity measurements of gas being swept out of the cavity to further confirm the wind.