A black hole breathing at the centre of the Milky Way has been discovered
Black holes are usually imagined as cosmic hoovers: anything that gets too close, they pull inside. But that's only part of the story. Around a black hole, some of the gas may not fall inside, but rather fly out.
Astronomers have been looking for such a "wind" in a black hole at the centre of our Galaxy for more than 50 years. It is called Sagittarius A* and is located in the centre of the Milky Way. Now scientists have found its trace: near the black hole is an area where there is almost no cold gas, as if it was blown out by a powerful cosmic hairdryer.
Importantly, nothing escapes from the black hole itself. Once matter has crossed its boundary, it doesn't come back. "Wind" appears near it - from the hot gas that circles around the black hole and is partially ejected outside.
Details
At the centre of the Milky Way is the supermassive black hole Sagittarius A*. It's huge, but it's pretty quiet right now. Unlike black holes in some other galaxies, it doesn't set off bright "fireworks" and doesn't look very active.
But theory has long said that even a quiet black hole should produce streams of gas. When matter falls towards it, it accelerates, heats up and becomes very energetic. Some of this gas may not fall in, but escape out. This kind of flow is what astronomers call wind.
The problem was that at Sagittarius A* this wind could not be seen. Looking into the centre of our galaxy is difficult: there is a lot of gas, dust and other structures between us and the black hole.
Now researchers have used data from the ALMA radio telescopes in Chile and the Chandra X-ray Observatory. ALMA helped them see the cold gas near the black hole, while Chandra showed the hot X-ray region.
As a result, scientists noticed a strange shape: a cone-shaped void in the cold gas. It stretches for about 3 light-years and opens up at about 45 degrees. In simple words, there is an area near the black hole where there should be more cold gas, but it's barely there.
Researchers believe this is the wind trail. The hot flow from the black hole could have either pushed the cold gas out or heated it so much that it is no longer visible as cold gas.
Why it matters
This discovery helps us understand that black holes don't just "eat" matter. They also change the space around them.
This wind can affect the gas at the centre of the galaxy: blowing it out, heating it up and preventing it from gathering into new stars. This is important to astronomers because black holes at the centres of galaxies can gradually change the life of the whole galaxy.
Sagittarius A* is particularly interesting because it's our cosmic neighbour. It's in our galaxy, so it can be studied in more detail than distant black holes.
The wind found does not mean a danger to the Earth. It's about processes at the centre of the Milky Way, very far away from us.
Background
Astronomers have long seen powerful jets and streams of gas at other black holes. That's why Sagittarius A* looked strange: it seemed like it should be blowing something out too, but no direct traces were found.
The new work closes part of this mystery. The scientists found not the "wind" itself as a flow of air, but its trace - an empty region in the cold gas. This is similar to a situation where you can't see the wind itself, but you can see how it dispersed smoke or dust.
Researchers estimate that this flow could have been active for at least 20,000 years. This is not a short burst, but a long process in the life of our Galaxy's central black hole.
Source
Thestudy: Mark D. Gorski et al, "The discovery of a large active wind from the Milky Way's central black hole", The Astrophysical Journal Letters, 2026.