G Objects: A Strange New Discovery At The Galactic Centre!

Unravel the mystery of G objects orbiting the black hole at the center of the Milky Way Galaxy. Discover their unique behavior.

Video of the day February 8th 2020


From what they are, to what they could mean for both black holes and the Milky Way Galaxy, join me as we unravel the mystery of G objects.

Sagittarius A: The black hole at the center of the Milky Way

So…what exactly are G objects? To answer that, we have to go to the center of the Milky Way Galaxy, you know, the galaxy we live in right now? Well, at the center of that is a black hole, or to be more accurate a “radio source” that we BELIEVE to be a Supermassive Black Hole known as Sagittarius A. We technically know it’s a black hole because of readings and such, but as many scientists like to note, if you haven’t seen it or touched it yourself…it’s all theoretical. 

Anyway, like you would expect from a black hole, the area around it is dark (as black holes don’t let light escape and thus they make a black mass of space) and anything that would get near it would get sucked in. But over the last few decades, astronomers have noted that there are things actually orbiting the black hole, which really shouldn’t be happening. And yet, they are, and they’re acting like objects that have never been viewed before in space or anything else.

Thus, these objects were labeled, “G Objects”, and of these objects that we have found, there are 6. There could be more, but we haven’t found them yet, so for now it’s just six, and the first two of these six were actually found decades ago.

Here’s what happened, scientists were studying the black hole and over the course of many years realized that two objects seemed to be orbiting the black hole, and yet, they weren’t acting right. The first belief of these objects in regards to what they were gas clouds. Which if we’re being honest would make sense as gas clouds are littered throughout space, including one that has the chemical that is used to make alcohol taste better (no, really, look it up.)

But there were some problems with this theory. First among them was that these two different gas clouds were 100 astronomical units across (one astronomical unit is the distance between the Earth and the sun), which made it REALLY weird that something that size would be orbiting a black hole without issue. And as they looked closer, they noticed that the clouds were getting stretched out as they were getting closer to the black hole. So in many ways, these gas clouds were acting like something else made of gas…

“These objects look like gas but behave like stars,” said physicist and astronomer Andrea Ghez of the University of California, Los Angeles.

G1 and G2: The initial discoveries

Since the find of G1 and G2 (the names of the two gas clouds), the team led by Ghez has been studying the center of the galaxy for 20 years! And through that, they found G3-G6, confirming that there were many objects orbiting Sagittarius A…for some reason. What’s even weirder if you can believe it is the orbits of these six objects aren’t uniform in the slightest, they are vastly different. No unlike the planets in our solar system having much longer orbits than Earth.

How different are they? Depending on the object they can range from 170 years to 1,600 years! And…yes, there’s more, there’s always more, they STILL don’t know what these six objects are! How’s that for a kicker?

We are getting clues though as to what some of them MIGHT be. For example, in 2014, the object known as G2 entered a period of its orbit where it was closest to the black hole, and when that happened, some observations were made:

“G2 is a dusty red object associated with gas that shows tidal interactions as it nears its closest approach with the Galaxy’s central black hole.”

Not just that though, as they observed it from that point to where it moved to next, scientists noticed that it was changing shape based on where it was near the black hole:

“We had seen it before, but it didn’t look too peculiar until it got close to the black hole and became elongated, and much of its gas was torn apart. It went from being a pretty innocuous object when it was far from the black hole to one that was really stretched out and distorted at its closest approach and lost its outer shell, and now it’s getting more compact again.”

So what does that tell us? What does this mean as a whole? Does it truly help us determine what G2 is, or what any of the other G objects are? 

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The answer to what the G objects may be might be simpler than you might suspect. Because it doesn’t necessarily have to do with what the G objects are per se, but rather, with where they are located!

Binary stars

Confused? I’ll explain. There are many kinds of stars in the universe, we’ve even talked about some of them here on the channel before, but one of those types of stars is Binary. Binary stars are defined as:

“A binary star is a star system consisting of two stars orbiting around their common barycenter. Systems of two or more stars are called multiple star systems. These systems, especially when more distant, often appear to the unaided eye as a single point of light, and are then revealed as multiple by other means.”

If you remember Tatooine from Star Wars? That was a Binary Star, they even named the classic theme when Luke Skywalker looks out at the stars as “Binary Sunset”. But I digress.

Anyway, these Binary Stars are usually very stable, and they’re more than happy to just keep orbiting each other until their time runs out, and most of the time that does happen. However, on occasion, they do collide with one another and when they do that, they make a massive star. End of story? Not so much, because this fusion has a lot of side effects if you will, and one of them is causing massive clouds of gas and dust to be formed. These clouds will go and circle the new star for millions of years.

And it is this result that some scientists think is G2, with a little bit of a twist of course…

“Something must have kept [G2] compact and enabled it to survive its encounter with the black hole,” Ciurlo added. “This is evidence for a stellar object inside G2.”

Basically, it means that in the vastness of G2 there is something like a star, possibly a fused Binary Star that is there keeping it compact as it travels, and then when it gets closer to the black hole, it gets stretched, yet when it’s further away from it, the stellar object brings it back to its compact shape.

This is important to note as plausible for a simple reason, in the center of our galaxy are a LOT of Binary stars, and these stars not only have a lot of gravity, they have a lot of mass. They’re HUGE! So when a Binary Star fuses together? The results would be incredible, including the gas and dust clouds that they make.

To that end, some scientists believe that the other G Objects are possibly also gas byproducts from fused Binary Stars.

“Mergers of stars may be happening in the Universe more often than we thought, and likely are quite common,” Ghez said.

Theories on the origin of G Objects

She went on to not that not only is it possible, but the black holes around the center of the Milky Way (alongside Sagittarius A) could be making them happen more than they would naturally:

“Black holes may be driving binary stars to merge. It’s possible that many of the stars we’ve been watching and not understanding may be the end product of mergers that are calm now. We are learning how galaxies and black holes evolve. The way binary stars interact with each other and with the black hole is very different from how single stars interact with other single stars and with the black hole.”

So is that it? Is that the end of the mystery of the G objects? That they’re just remnants of merged Binary Stars and that they’re just being pulled in certain ways by the black hole and other stars around it?

Uh…not quite. Because while this is a good theory, and one backed by science and what we know of the universe, Sagittarius A has shown that we don’t know everything that’s going on in this area. Which means that any assumptions about the G Objects, no matter how logical, is likely still very incomplete.

By this, I’m referring to an incident that happened in 2019 where Sagittarius A suddenly grew very bright on infrared scales, very much akin to a “fireworks show” going off:

“The black hole was so bright I at first mistook it for the star S0-2, because I had never seen Sgr A* that bright. Over the next few frames, though, it was clear the source was variable and had to be the black hole. I knew almost right away there was probably something interesting going on with the black hole.”

So for some reason, this supermassive black hole just decided to flare up for no apparent reason, and to be clear, we STILL don’t know what could have caused these things to happen, or why they happened at that point in 2019:

“We have never seen anything like this in the 24 years we have studied the supermassive black hole,” said Andrea Ghez, UCLA professor of physics and astronomy and a co-senior author of the research. “It’s usually a pretty quiet, wimpy black hole on a diet. We don’t know what is driving this big feast.”

Usually, when that kind of flare up happens it’s due to an object being caught into its orbit and being sucked into the black hole. But the problem with that known quantity here is that…there wasn’t anything near the black hole that could’ve been sucked up. So thus, the scientists had to look elsewhere for possible theories and solutions to the problem:

“One of the possibilities,” Do told ScienceAlert, “is that the star S0-2, when it passed close to the black hole last year, changed the way gas flows into the black hole, and so more gas is falling on it, leading it to become more variable.”

The role of black holes in stellar evolution

But again, that’s just one belief, and it’s one that hasn’t necessarily be proven yet. Yet you might be asking, “How does this apply to the G Objects?” It’s simple that for all we know, it’s the black hole itself that are causing the G Objects to be born, or orbiting itself like they do. Many people are curious about these objects because they orbit the black hole that is the center of our galaxy, but what if it’s the black hole itself that caused them to be born? 

This is not unheard of. In fact, there is a real-life object that is known to come FROM the black holes in our universe. As a matter of fact, one of them is confirmed to have come from Sagittarius A itself, it’s known as a hypervelocity star.

These are stars that are somehow ejected from the black hole (like Sagittarius A) and sent careening into space at speeds over 2 million miles per hour! What’s more, unlike other stars that tied to the “tether” of the galactic pull, these stars aren’t held by that, and thus can shoot through space into places we can’t even fathom right now at a really good clip.

How do black holes create hypervelocity stars? We have no clue.

The best theory we have is that sometimes Binary Stars are swallowed up by supermassive black holes, and while one is fully devoured, the other is shot out at speeds that boggle the mind in regards to the size of a star. But the problem is that his is known as an “exotic phenomena”, meaning it doesn’t happen all the time, and thus it’s REALLY hard to prove that this is what happens here.

Still, we do know that Hypervelocity Stars exist, and that they seem to emanate from black holes, so if the black hole could create something like that, what’s to say it can’t have somehow created whatever these G Objects are?


What’s more, looking out at the vast reaches of space itself, we still don’t know what all is out there. There are NUMEROUS mysteries that haven’t even come close to solving, including some things that are within our very own solar system. So while it may seem like these G Objects may be something as simple as clouds of gas and dust, that might not be the case. 

They could be something that we honestly just haven’t discovered yet, or know about yet. I mean, we’re still finding moons around our neighbor planets, and we think we know what’s going on at the center of our galaxy that we can only see through still frames and certain sensors? …I don’t think so.

But, IF we are to find out what’s going on at the center of the galaxy, this could be a great clue as to what is going on at the center of other galaxies, which are all thought to have supermassive black holes like Sagittarius A. So just imagine what these G Objects could reveal if we are able to see what they truly are?

The mysteries of space continue to grow, and that’s why people love looking up at the stars.

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