Sagittarius A*: The Invisible Giant We Are All Orbiting

Indexado: 2026-05-22

[00:00:02]Right now, while you're watching this, the Earth is moving at about 30 km/s through space. And that is still the slowest movement we are currently involved in. Our entire solar system, meaning the sun, all the planets, everything, is racing at roughly 220 km/s through the Milky Way in the direction of a point in the constellation Hercules that we call the solar apex. And the strangest part about it, we don't feel any of it.

[00:00:34]But where are we actually moving? And what is pulling us? At the center of our galaxy sits something, something that cannot be seen. Something that is so heavy that stars circle around it with incredible speed. We circle around it too for billions of years. And to understand what exactly is sitting there in the center, you first have to understand why we couldn't see it at all for so long. Approximately 26,000 lightyears away from us lies the center of our galaxy. You cannot see it. Not because it is too far away, but because between us and the center lies so much stuff. Dust clouds, gas clouds, billions of stars that visible light simply does not get through. As if you were trying to look through a wall of fog. Nothing.

[00:01:28]For decades, we simply did not know what was going on over there. Only when we started observing with infrared and radio waves, meaning with light that we cannot see ourselves, did it slowly become clearer what sits there. It is called Sagittarius A. An object with the mass of about 4 million suns compressed into an area that is smaller than our solar system. It emits no light. It reflects nothing. It is simply there and everything around it reacts to its gravity. 4 million solar masses sounds abstract, but imagine our sun is already 333,000 times as heavy as the Earth. And Sagittarius A has the mass of 4 million of such suns that sits at the center of our galaxy and pulls on everything. But wait, if it is invisible, how do we even know that it exists?

[00:02:29]A black hole emits no light. It reflects none. Nothing that falls in ever comes back out. That means direct observation is impossible. You cannot photograph it, illuminate it, or measure it like a normal star. So, we did the only thing left to do. We looked at what happens around it. In the '90s, researchers began observing stars in the center of the Milky Way over decades. And these stars were moving, not slowly, not randomly. They were orbiting in tight, fast paths around a point where apparently nothing was. One of these stars is called S2. S2 takes about 16 years for a complete orbit. For comparison, the Earth takes 1 year to orbit the Sun.

[00:03:21]In 16 years, S2 orbits something that is about 4 million times heavier than our sun. And that in a tight space, at its closest point, S2 gets so close to the center that it accelerates to nearly 3% of the speed of light. 3% sounds like little. It is still almost 9,000 km/s.

[00:03:44]No normal object could cause that. No star cluster, no invisible gas cloud, nothing. The only explanation that physics allows is a super massive black hole. That is the proof, not a photo, but the movement of stars around something we cannot see.

[00:04:06]However, it must be said that while we orbit Sagittarius A, we are not directly pulled by it. From 26,000 lighty years away, we notice nothing. The gravity of Sagittarius A is so weak at this distance that it has no measurable influence on us. We orbit the center of the galaxy. But that is due to the total mass of the Milky Way, not the black hole alone. If we were closer, that would be a different story. In the center of the Milky Way, stars lie so densely together that the night sky from there would look like a single shining chaos. No dark background, only light in all directions. That alone would already be deadly. The amounts of radiation there are enormous. And then there is the black hole itself.

[00:05:01]Black holes do not necessarily kill through heat or radiation. What makes them truly dangerous are tidal forces.

[00:05:10]Gravity pulls harder on the part of you that is closer than on the part that is further away. This difference tears things apart. There is even a name for it, spaghettification.

[00:05:23]What happens is exactly what the name suggests. Matter is stretched out thinner and thinner until it is drawn into the black hole in a long thread.

[00:05:33]With Sagittarius A, that would happen relatively close to the boundary. With smaller black holes, even before that, before you even reach this boundary, so you would not fall in and then die, you would be torn apart on the way there slowly from your own perspective. For someone watching from the outside, you would simply freeze, get stuck at the boundary forever. That is because time at such a place plays almost crazy due to its enormous gravity. But that is theory. No human has ever really been close. What we have managed to do, however, is a photo.

[00:06:18]In 2022, a photo was published. A blurry orange ring in the middle. Darkness.

[00:06:25]That was Sagittarius A, not the black hole itself. You don't see that by definition. What you see is the material around it. Gas and dust orbiting the black hole so fast and getting so hot in the process that it glows. The dark middle is the shadow. The area from which no light can escape anymore. The image seems unspectacular if you don't know what is behind it. A single telescope could never have captured it.

[00:06:57]The resolution needed for this is roughly like wanting to recognize a single orange on the moon from Earth.

[00:07:05]That is not possible with a normal telescope. So astronomers didn't use one. Instead, they distributed telescopes all over the Earth in Spain, Hawaii, Antarctica, and pointed them all at the same spot at the same time.

[00:07:22]Together they form a telescope as large as the Earth itself. This is called the event horizon telescope. Sagittarius A was particularly difficult to photograph, not because of the distance.

[00:07:37]M87, the black hole in another galaxy, is much further away and was already photographed in 2019.

[00:07:46]The problem is that Sagittarius A is constantly changing. The material around it moves so fast that the image changes within minutes. As if you were trying to take a photo of something that never stands still. The solution was to combine thousands of individual shots and then mathematically figure out what the object looks like on average. The result, this blurry orange ring. For decades, we only knew that something was there. Now we have at least this. But Sagittarius A was not always as quiet as it is today. Because yes, currently it is relatively quiet. It occasionally swallows something, gas, dust, sometimes a star that gets too close. But compared to black holes in other galaxies, it is significantly quieter. There are indications that it used to be different.

[00:08:43]When a black hole is active, meaning when it swallows large amounts of material, it releases enormous amounts of energy in the process, radiation, particles, outbursts. This leaves traces. And exactly such traces we have found above and below the Milky Way perpendicular to the dis of the galaxy stretch two giant bubbles of hot gas.

[00:09:11]Each of them is about 25,000 lighty years large. They were discovered in 2010 by the Fairmy Space Telescope and have been called Fermy bubbles ever since. No one knows with absolute certainty where they come from. But one of the most likely explanations is that Sagittarius A had a massive outburst millions of years ago. An event in which so much energy was released that it blew the matter above and below the galaxy into these giant structures. That would have been an outburst that affected the entire galaxy.

[00:09:51]Today, Sagittarius A sits quietly in the center, but these bubbles are still there as an imprint of something that happened a long time ago and that we are only now slowly understanding. What all this together means is actually the most interesting part. There is a thought that easily gets lost in this.

[00:10:12]Sagittarius A is not the reason why we stay in the Milky Way. As I just said, it is not the anchor that holds everything together. 4 million solar masses sound like a lot, but the Milky Way has a total mass of several hundred billion suns. The black hole at the center is measured against the entire galaxy. A tiny fraction of it. What truly holds us is everything together.

[00:10:39]Billions of stars, gas clouds, dust, and then something else that we haven't been able to directly observe to this day.

[00:10:49]Dark matter. A substance that emits no light, reflects none, and moves through normal matter as if it weren't there. We know it exists because without it, galaxies would physically make no sense.

[00:11:03]They would rotate too fast and fly apart.

[00:11:08]So, there is something else. We just don't know exactly what. Sagittarius A sits right in the center of this entire mass. It is like a marker, an extremely heavy point that shows where the middle is. And we orbit this middle not because of a single object but because of the gravity of an entire galaxy that has kept us on this path for billions of years. Every second you have ever lived, every morning, every evening, all of it happened while we were racing through the Milky Way at hundreds of kilome per second. For decades, Sagittarius A was nothing more than a strange radio signal from the direction of Sagittarius. No image, no proof, only clues.

[00:11:55]Stars that move strangely, calculations that pointed to something invisible.

[00:12:01]Only in 2022 did we have an image, a blurry ring, after decades.

[00:12:10]I hope you enjoyed the video and see you next time.