For more than 50 years, astronomers have searched for a powerful wind blowing from the supermassive black hole at the center of our galaxy.
Now, a team of researchers from Northwestern University has finally found convincing evidence that this long-suspected wind exists.
The black hole, known as Sagittarius A* (Sgr A*), sits about 26,000 light-years from Earth at the heart of the Milky Way.
Scientists have long believed that black holes do more than simply swallow matter. As gas and dust spiral toward a black hole, some of that material should be blasted back into space as winds or jets.
This process has been observed around many other black holes throughout the universe.
But despite decades of searching, astronomers could not find clear evidence of such a wind around Sagittarius A*.
If no wind existed, our galaxy’s black hole would be very different from those found elsewhere in the universe.
Using new observations from the Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile, researchers finally uncovered the missing evidence.
By analyzing five years of extremely detailed observations, they created the sharpest image ever made of cold gas surrounding the black hole.
The team focused on clouds of cold molecular gas located within about three light-years of Sagittarius A*. To reveal faint details hidden in the data, they developed techniques to remove the bright radio signals produced by the black hole itself.
What emerged was a surprising discovery: a giant cone-shaped cavity where cold gas was missing. The hollow region stretches nearly three light-years long and spans about 45 degrees across.
According to the researchers, the most likely explanation is a hot wind blowing outward from the black hole. As the wind travels through space, it either pushes cold gas away or heats it so much that it can no longer be detected.
The scientists ruled out nearby stars as the cause. While stars produce their own stellar winds, calculations showed that even all the stars in the area combined could not generate enough energy to create such a large cavity. The cone also points directly back toward Sagittarius A*, strengthening the case that the black hole is responsible.
To confirm their findings, the team compared their results with previous observations from NASA’s Chandra X-ray Observatory. They found bright X-ray emissions in exactly the same region where the cold gas was missing. This provided an important independent line of evidence that a powerful outflow was shaping the area around the black hole.
The researchers estimate that the wind has been active for at least 20,000 years. Although it is not especially powerful compared with the dramatic jets seen in some galaxies, it is exactly the type of outflow scientists expected from a black hole in a relatively quiet state.
The discovery offers valuable insight into how black holes behave when they are not actively feeding at high rates.
Many studies focus on extremely active black holes that produce spectacular bursts of energy. However, astronomers believe most black holes spend much of their lives in quieter phases.
By finally detecting Sagittarius A*’s hidden wind, scientists now have a rare opportunity to study what a supermassive black hole looks like during one of these calmer periods.
The finding not only solves a long-standing mystery but also helps researchers better understand the role black holes play in shaping galaxies throughout the universe.
