Invisible Force at the Center of the Milky Way Finally Found

[00:00:00]For 50 years, astronomers searched for something invisible at the center of our galaxy. It's almost impossible to detect, yet powerful enough to reshape the Milky Way. Now, they may have finally found it. And it's not a new star or a planet. It's a wind coming from the super massive black hole Sagittarius Aar. And it might be carving a giant cavity in space.

[00:00:30]So, black holes just don't pull things in. Sometimes they blow things away, too. When gas and dust fall toward a black hole, they don't drop straight in.

[00:00:42]They start spinning around it at crazy speeds like water circling a drain. All that motion creates a huge amount of heat. And the hotter it gets, the more energy gets blasted back into space.

[00:00:57]When you throw wood into a campfire, the fire doesn't just burn the wood. It also throws out heat, smoke, and sparks.

[00:01:05][music] A feeding black hole does something similar. When it gobbles up material, it produces immensely powerful streams of gas that dash outward. Basically, a kind of cosmic wind. Astronomers see these winds around super massive black holes all over the universe. Then what about the black hole at the center of our own galaxy? Sagittarius A star is a super massive black hole with a mass about 4 million times larger than the sun. At the same time, it's surprisingly compact. If you placed it in our solar system, it would easily fit inside the orbit of Mercury. In 2022, scientists finally captured the first image of it.

[00:01:54]Not the black hole itself. It's impossible to see because no light can escape it. But they managed to photograph the glowing ring of superheated gas swirling around the hole at incredible speeds. This makes the black hole look like a giant burning donut floating in space. In any case, if black holes produce winds, ours is massive enough to create some, too. even though it's barely eating anything right now. And still for more than 50 years, nobody could find this wind. Even when bigger telescopes and better instruments came, the wind was still missing.

[00:02:36][music] The problem is that we were trying to look through our own galaxy where huge clouds of gas and dust sit [music] in the way and block most of the view. It's a bit like trying to spot a flashlight through a thick fog. But now that long search may finally be over. A team of researchers from Northwestern University claims they've finally found it. If it's so, we might be able to see what that super massive monster at the center of our galaxy [music] is actually doing. Finding that wind wasn't easy.

[00:03:13]For one thing, astronomers had to [music] look straight through the thickest part of our galaxy with all kinds of glowing clouds and other stuff floating around in the way. And we couldn't rule out the possibility that Sagittarius AAR wasn't producing any detectable wind at all. But this idea didn't seem believable. A black hole doesn't need to be actively swallowing stars to create a wind. As long as some material is falling toward it, there should be at least a small outflow. Now, the universe doesn't really do perfect emptiness. Even the emptiest regions [music] still contain a few particles here and there. And Sagittarius A star exists inside a galaxy full of gas and [music] dust. So, it should be blowing something outward. The challenge was finding it until researchers finally spotted a clue. It wasn't the wind itself yet. They found the mark it left behind. Near our black hole, they [music] discovered a huge gap in the surrounding gas. Something seemed to have pushed that gas away, [music] and the most likely culprit was the black hole. Astronomers already knew there was a lot of gas near the center of the Milky Way. Most of it sits in a giant ring around the black hole. It's like a huge cosmic traffic circle made of gas.

[00:04:44]But for years, scientists believe that the area closer to the black hole was mostly empty of cold gas because they only saw hotter gas there. Then our astronomers used ALMA, one of the [music] most powerful radio telescope systems on Earth. And they found something unexpected. There was much more cold gas near the black hole than anyone thought. To track it down, they followed carbon monoxide gas. That might sound strange, but researchers use carbon monoxide the same way detectives use footprints. It's one of the easiest ways to see where cold gas is hiding in space. Once they started mapping this gas, [music] the astronomers noticed something odd. A huge chunk of it was missing. Right next to the black hole, they found a giant cone-shaped gap stretching more than three light years into space. That's almost 20 trillion miles, nearly 200,000 times more than the distance between the Earth and the Sun. And the researchers think it was the black hole's wind that gradually blasted that gas out of the way. But the team still needed proof. So they started checking other possibilities. Maybe a nearby star had blown the gas away.

[00:06:09]Well, that [music] didn't work. The empty region was simply too large. Even [music] if you combine the winds from all the stars near the center of the galaxy, they still wouldn't have enough energy to create such a giant gap. Well, maybe it was a massive stellar explosion. Nope. The shape didn't match.

[00:06:30]The gap wasn't random. It formed a huge cone. And that cone pointed straight back towards Sagittarius Aar.

[00:06:40]That's when the team found another clue.

[00:06:43]NASA's Chandra [music] X-ray Observatory had already been studying the same region. And when the researchers compared the data, they noticed that the cone-shaped gap lined up with a source of [music] X-rays. That was exactly what they wanted to see because hot gas from the black hole would produce X-rays [music] as it moved through space. The pieces started fitting together. The giant cone, the missing cold gas, the X-rays, and the direction of the structure. Every clue pointed to Sagittarius AAR and the wind it produces. But don't imagine a giant blast, a cosmic [music] hurricane shooting across the galaxy. This wind is actually pretty weak compared to the powerful jets some black holes produce.

[00:07:35]The researchers also think that the wind doesn't always blow in the same direction. Over time, it shifts and pushes gas around different areas near the black hole. That's why the coneshaped cavity isn't perfectly symmetrical. And still, even though the black hole wind itself isn't particularly dramatic, the fact that it exists means that our cosmic neighborhood isn't some special windless exception. The super massive black hole sitting at the center of the Milky Way [music] apparently follows the same rules as everyone else. This discovery won't change our lives, at least not [music] directly. After all, the wind is happening about 27,000 light years away near the center of [music] the Milky Way. Nothing from it is going to reach Earth. But it's important because it can help us figure out how black holes affect the galaxies around them and why some galaxies keep making [music] new stars while others stop. We might even find out how galaxies change over billions of years. You see, scientists think black holes are one of the main things shaping galaxies. But to make sure it's true, we need to understand how black holes interact with the gas around them. And the newly discovered wind might be part of that puzzle. Most super massive black holes in the universe spend most of their lives in a quiet state just like Sagittarius AAR.

[00:09:12]The problem is that those black holes are usually millions or even billions of light years away. They're simply too far away to study in detail. Astronomers usually notice distant black holes only when they're extremely active, when they're swallowing huge amounts of material. That's like trying to understand how people normally live by only watching them during carnivals.

[00:09:38]Sagittarius AAR gives us something we've never had before. A close-up look at what a super massive black hole does during its ordinary quiet life. And if our black hole behaves this way, there's a good chance that countless other quiet black holes across the universe do exactly the same thing.

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