Astrum Space - We Found Something Unexpected at the Heart of the Milky Way

Episode Date: September 30, 2026

This Astrum supercut is a complete guide to the Milky Way. We’ll dig into the weirdest discoveries in our own cosmic backyard, reveal the mysterious structures hiding at the galactic centre, and find out what our home galaxy really looks like. If we can map galaxies billions of light-years away... why is our own home still such an enigma?To those returning and new to the channel: This video is a supercut of Astrum’s best videos about the Milky Way, plus new and updated content. We’ve edited this into a new seamless video, remastered in 4K resolution, and re-recorded the older voiceover to match the quality of the recent episodes.▀▀▀▀▀▀The Astrum book is still available in the US! Get your hands on one here: https://astrumspace.co/ A huge thanks to our Patreons who help make these videos possible. Sign-up here: ⁠https://bit.ly/4aiJZNF

Hear that? It's your money calling. It wants a promotion. Elevate your savings with the Scotia high-interest savings account. Always earn high regular interest rates that grow the more you save and invest. Conditions apply. Visit scotiabank.com slash h-I-SA to learn more. Scotia Bank. You're richer than you think. You may think you know our Milky Way galaxy, but trust me, you don't. for something that is all around us.

We know less about our galactic home than we know about galaxies that are millions of light years away. It is apparent that birthed us and yet keeps much about itself an enigma. It is filled with wonders. And yet those very wonders dazzle us, meaning the secrets that lie on the other side

have remained hidden for millennia. That is, until now. Towering filament structure. incredible star formations, black holes and supernovae, and evidence of ancient interlopers. With the aid of powerful telescopes that have worked tirelessly to collect data over the last few decades, the mysteries of our own Milky Way galaxy are finally being revealed. Are you ready to see what they've uncovered? I'm Alex McColgan and you're watching Astrum, and today in this supercutt, with the aid

of some of the most extensive star maps to date, we are going on a tour of the Milky Way like you've never seen it before. Here's a fun question to start with. What does the Milky Way actually look like? This simple question does not have an easy answer. As I already alluded to, looking at our galaxy is surprisingly hard. Our Milky Way galaxy is a massive collection of 100 to 400 billion stars, 100,000 light years across, with great seas of interstellar clouds and gas, and all that matter

can get in the way of what we're trying to look at. This gets particularly bad towards the center of the Milky Way's plane, where the most matter accumulates, creating an area astronomers referred to as the zone of avoidance. Visible light cannot easily penetrate this zone, leading scientists to resort to other mediums like x-rays to scrutinize what lies beyond. It's like how it's easier to look out your window at the house across the street than it is for you to look at your own house from that same position. You might be able to see the four walls of the room immediately around you, but good luck trying to figure out the layout of the rest of the house with those same walls getting in your

way. Further compounding this is the difficulty in telling how far away a star is from Earth. To make a 3D map of the Milky Way galaxy, you need to know if the stars you can see are dim, small, close ones, or large, bright, distant ones that only look dim and small because of their distance. Not all stars make this easy, while some types of stars such as sepheid variable stars have a predictable enough luminosity that their distance can be calculated if you know a few things about them, not all are quite as accommodating. So our Milky Way is surprisingly hard to map out, hence why we are not even sure exactly how many stars are here. The scientists have worked hard to solve this embarrassing gap in our knowledge. So for unpredictable stars, how can you tell how far away they are? The answer is parallax. And that's what our first telescope, Gaia, used as it created a galaxy map over the course of 11 years.

Parallax is the principle that, depending on your point of view, things can appear to be in different places. You can see an example of this right now by holding up your finger in front of your face. Close one eye, then instead close the other. Now alternate quickly between the two. See, your finger moves quite significantly in relation to its background. The closer an object is, the greater the effect of parallax. Simple trigonometry takes care of the rest, allowing you to calculate how far away an object is. While this effect was very noticeable based on a finger in front of your face, you'll see much less parallax on a tree on the other side of a field, which means it's further from you. The further away something

is, the harder it is to use parallax to tell you its distance. Things can get a little imprecise. But how then can we use this method to calculate the distance to a star? The secret is to widen your base viewpoint. Just as the distance between your eyes can influence the effect of parallax on an object, Gaia viewed stars not just once, but multiple times over the course of a decade. In that time, the face of our night sky will have changed, as we can see in time lapses like this one, with an exaggeration of 10,000 times. Rather than using the six centimeters between your eyes as the base. Every half year we can make the solar system our base instead. Our Earth moves from one side of the sun to the other, which causes

parallax effects to be visible in every star we see. Note how in this animation the stars are taking little looping patterns? That's not really how they're moving, but how we are. That's the effect of our own loops around the sun. This can help with measuring stars. distance, but there's actually an even larger scale we can use. The proper motion of stars. We can ignore the loops for this one as an even larger base is coming into play. Rather than just use the motion of our planet on either side of the solar system, we can make use of the fact that our own solar system, along with the other stars in the galaxy,

are also moving. So we can use that motion as an even larger base for establishing parallax. The same principle applies. Stars with proper motions against the backdrop of space are closer, while stars with less proper motion are further away. In this way, Gaia had been building a precise 3D map of 2 billion stars in our Milky Way galaxy and beyond over the course of 3 trillion observations.

But Gaia had not just been looking at their motion and distance. His mission for this telescope was to study the luminosity, temperature, mass, and chemical composition of these stars too. It housed two powerful telescopes that channeled light from two different directions into a camera with nearly a billion pixels. At the time, the most precise camera in space. Its radial velocity spectrometer could measure Doppler shift to give us clues about its velocity. It also had photometric instruments to reveal spectral information about each star.

properties like composition and temperature. So although 2 billion stars is only a drop in the ocean of the 100 billion stars thought to inhabit the Milky Way, this still allowed us to create an incredibly detailed map of our galaxy over time. And it's that over time bit that allows us to see the Milky Way's eating habits. You see, our Milky Way turns out to be hungry for sausages. Yes, sausages. But no, not the meaty kind.

Allow me to explain. For over a decade since 2013, when Gaia was launched, it collected data which ESA scientists have been processing and releasing in large data packets for the general scientific community to study. The larger the gap in time, the more comprehensive and precise the data. More time equals more parallax. Three such data releases have taken place so far. In 2016, 2018, and a two-parter that released a simplified version in 2020 and then the full version

in 2022. And scientists have already had the chance to evaluate what Gaia has seen. And as they witnessed the motions and locations of stars in our galaxy over time, it became possible to model the whole galaxy and even wind it backwards. Take a look at this. It's impossible to photograph our own galaxy, as no camera-equipped spacecraft has traveled out that far, but here is a representation created using Gaia's data of what it looks like to an unprecedented degree of accuracy.

Note its wobbly edges. These indicated to scientists that the Milky Way crashed into another galaxy in the distant past. the second data release, researchers from the Netherlands looked at 7 million stars and found that 30,000 of them were moving strangely. While most stars, including our own, move around the Milky Way in one direction, this odd collection was moving the opposite way. Their colour and brightness were also strangely distinct, indicating there was something special about this particular group.

The researchers ran the numbers and found that a model was a model of the different, and found that a model that fitted their observations was what would happen if another galaxy collided with our own. The collision must have happened 8 to 11 billion years ago and involved a small dwarf galaxy that the researchers called Gaia Enceladus, or sometimes the Gaia Enceladus sausage. See, I told you. See how its stars indicated here in red actually managed to retain a fairly discreet form for a time, before eventually spreading out across the Milky Way. This merger may have been an important part of how our Milky Way came to have some of its unique characteristics,

such as a bar in the centre, something that only two-thirds of spiral galaxies have. The Milky Way didn't go in for a little late-night sausage-eating just once, though. Another dwarf galaxy, known as Arruya, Sequoia, Litoi, was also found to have merged with the Milky Way. way, and perhaps was a binary pairing with Gaia Enceladus. And then, in a later study, another dwarf galaxy's remnants were found, more than one, in fact. According to this study, our Milky Way may have eaten as many as six other galaxies. Gaia data reveals this hasn't stopped. The nearby dwarf galaxy Sagittarius has collided with our own three times already in

the past four to five billion years. and is set to do so again. This collision may have even been the spark that lit the flame of our very own sun, which came into being around that same time. Eventually, Sagittarius may well become galaxy number seven that the Milky Way has consumed, all of its stars being slowly ripped away and brought into our own galaxy. These revelations are just some of the incredible discoveries made possible. through the Gaia telescope's data, which is why it is sad Gaia's time came to a close.

The Gaia Telescope maintained its position in the second Lagrange Point using judiciously applied cold gas repellent a dozen grams a day. However, that cold gas, sadly, eventually ran out. On the 15th of January 2025, Gaia took its last observation and began the process of doing a few last calibrations before finally powering down on the 27th of March 2025. But its story is not over yet. Two more data packets await release. The first of the two, data release four, will include 500 terabytes of information and will be released on the 2nd of December, 26. It will only cover the first 5.5 years of Gaia's mission, but will do so to an incredible level of detail. Its precise measurements of stars wobbling motions might even

highlight possible locations of exoplanets and will create the largest catalogue of binary stars to date. It's also worth recognizing that the Discovery Sky brought us don't end with just prior or ongoing galaxy impacts. It's possible to fast forward the data to model the motion of our local stars millions of years into the future. allowing us to see incredible models like this one. Note how although the stars near us initially spread out across the Milky Way, they later reconvene due to what is thought to be density waves. Seeing this play out helps explain the spiral arm shape of our galaxy.

Gaia data has helped improve our picture of events much closer to home too. Gaya revealed the position and direction of travel of over 150,000 asteroids in our solar system. And thanks to its ability to track those movements over time, Gaya was able to demonstrate that 352 of them probably have moons, as shown by slight wobbles in these asteroids trajectories. This nearly doubled the number of such binary system asteroids that we were aware of. Gaya has been called a treasure trove, and it's hard to overstate just how much information can be found in these data releases.

Gai has provided us with what was at the time the largest ever 3D map of quasars across the wider universe, identifying 1.3 million of them, with the earliest being spotted at the edges of the universe, with light that started traveling when the universe was only 1.5 billion years years old. Gaia has found a previously unknown black hole in our Milky Way, 33 times the mass of the sun and only 2,000 light years away from us. This type of black hole had never been seen in our galaxy before. Most local black holes are only 10 times the mass of the sun, making this new find truly

massive. Many more such discoveries can be found thanks to Gaia data. No surprise that Issa is already considering plans for a Gaia replacement, Gaia NIR, a space telescope similar to Gaia, but able to see much further into the infrared to peer through the gas clouds that obscured Gaia's vision. But don't hold your breath for this one. If it goes ahead, Gaia NIR will look to launch in 2045 to provide an appropriate gap between that mission and Gaia, to allow Issa to take even more advanced.

advantage of parallax effects, Gaia NIR will be able to see how much further Gaia's observed stars have travelled in the intervening time. When it comes out, data release 5 will be the big one. Tentatively set to be released by the end of the decade, this data release will include everything, all 10.5 years of Gaia's mission to the highest level of detail imaginable. It will truly be a treasure trove of information. Just think what discoveries can be made with so much raw data to sift through. Who knows what else we will learn about our galaxy?

So while Gaia's mission coming to a close is sad, the wealth of data it has collected is also very exciting. Our Milky Way galaxy might be surprisingly hard to learn about, but Gaia's data will give us the best crack at it to date. Lucky for us. Geyer is not the only powerful telescope with goals to map out the Milky Way. And unlike Geyer, which focused on visible light, our next telescope looks at light that's invisible to the naked eye.

After all, the universe is full of secrets, and some of the most incredible ones are hiding just beyond the reach of visible light. What if I told you that more than 1.5 billion unseen objects, from galaxies and newborn stars to some of the oldest stars in our entire galaxy are sitting just out of reach of us, cloaked in cosmic dust. That's a little frustrating to think about, isn't it? Until now that is, because thanks to the European Southern Observatory's Visible and Infrared Survey Telescope for Astronomy,

better known as Vista, we can finally lift the veil. on these hidden wonders. For the first time in human history, we have a pretty comprehensive infrared map of the Milky Way, one that pierces through the obscuring fog of space to reveal an unprecedented view of our galaxy and what lies beyond. In September 2024, Vista published the largest and most detailed infrared survey of the Milky Way ever undertaken, encompassing a 13-year period from 2010 to In 2023, across 140 nights of observation, this project has captured around 200,000 images and generated 500 terabytes of data. That's the same amount of data as it would take to stream a 4K video for nearly three years

straight. Vista is part of ESO's Paranel Observatory located in Chile, with its main focus being to map large areas of the sky. Using Vista's infrared camera, known as Vercam, the team was able to peer through the dust and gas that permeates our galaxy and uncover some of the Milky Way's most hidden places. Traditional telescopes allow us to view space in visible wavelengths, which range between about 380 to 700 nanometers. But Vista isn't like traditional telescopes.

Instead of relying on visible light alone, Vista operates at infrared wavelengths between 900 and 1,200 nanometers, allowing it to detect otherwise invisible objects like stars obscured by dust and cold brown dwarfs, also known as failed stars, which don't emit enough visible light to be seen with a traditional telescope. To get an idea of the difference between visible and infrared light, take a look at these two images of the Lobster Nebula, or NDC-6357, one taken invisible light and the other with Vista's telescope. We can see that in the infrared, the dust that obscures our field of view seems to disappear,

revealing what look like hundreds of thousands or maybe even millions of previously invisible stars. And what it shows us about the Milky Way is incredible. The map we're looking at today was created through Vista Variables, or VVVVS survey, via Latvia, being the Latin name for the Milky Way, and its companion project, the VVVVE extended survey, or VVVVX. The data collected from these two companion projects that make up the Vista infrared survey have already led to the publication of more than 300 scientific articles. Unlike other recent space maps, this is one of the most detailed ones ever made. It's the first infrared survey to cover nearly 80% of the Milky Way's luminous mass, and provides the largest infrared catalog ever made of our galaxy's central region.

It allows astronomers to study our galaxy in finer detail than ever before. This survey gives us an accurate 3D view of the inner regions of the Milky Way way, which were previously hidden by dust. It covers an area of the sky equivalent to 8,600 full moons and contains about 10 times more objects than any previously published infrared map from 2012. When you're a mid-sized business, you need every competitive advantage you can get, like an AI solution that works for you, not against you. SAP Grow is built with AI embedded at its core, working across every system, and it's ready to go from day one so you can hit the ground running. Bring it with SAP Grow, AI Cloud ERP for any size business.

Hear that? It's your money calling. It wants a promotion. Elevate your savings with the Scotia high-interest savings account. Always earn high regular interest rates that grow the more you save and invest. Conditions apply. Visit scotiabank.com to learn more. Scotia Bank, you're richer than you think. Our Milky Way consists of a central bulge, a dense, bright, puffed-up collection of stars, with a flat disk of two main spiral arms and two minor ones wrapping from the ends. This image shows the area of our galaxy that was mapped in the survey. The red squares mark the central regions of the galaxy, which were observed by the original

survey and then re-observed again by the extended survey. And the other square colours show areas that were only observed as part of the extended survey. From this image, you can see that these surveys have focused right on the central plane of our galaxy, spanning part of the disk and most of the nuclear bulge. But what has Vista revealed? Argentinian astrophysicist Dante Miniti, who led the survey project, said, We've made so many discoveries, we have changed the view of our galaxy forever. And as much as I'd love to talk about all of them in this video, it's probably best I stick to some of the highlights.

As part of the survey in 2015, Vista turned its attention to the star formation region of Messier 20, also known as the Trifid Nebula, which lies about 9,000 light years from Earth. Viewed invisible light in this image, we can see a beautiful nebula, glowing pink from the emission of ionized hydrogen and surrounded by a blue haze of scattered light from young hot stars. The cloud of gas and dust is obscuring the star-filled space behind it. Now look at this second image taken by Vista's infrared camera. Peering beyond the clouds reveals a whole swarm of new stars. This image not only allows us to see through the Trifid Nebula, but by chance, it revealed objects on the far side of our galaxy that had never been seen before.

To their surprise, astronomers identified two faint, reddened objects as sea-feed variable stars. While they appear in the image to be just behind the edge of the Trifid Nebula, in reality they are very distant, about seven times farther than the nebula that once helped to block them from our view. Earlier we mentioned sephiard variables, a type of bright star that is unstable. They brighten and fade over a period of a few days, or a few months, depending on their brightness. The first variable star we ever identified in modern times was Omricon SETI, also known as mirror. It had been described as a Nova until 1638 when Johannes Hallwoods observed it getting brighter and dimmer in a cycle that lasted 11 months. As for this pair of newly discovered stars, they are

the only sea feed variables that we have identified so far in this location, which lies beyond the central bulge on the far side of our galaxy. And thanks to our ability to calculate the distance to them. They can be really useful too. You can think of them as a kind of cosmic yardstick that can be used up to distances of tens of millions of light years. If you know how long the star's pulsation period from bright to dim is, then you can infer its absolute brightness as well as its age. You can compare absolute brightness to the apparent brightness, that is, the amount of light that reaches Earth, so you have a measure of how distant the star is. With a few reference points like these, we can build up a real picture of the scale of our galaxy and beyond. Looking toward the

galactic center, a team of astronomers and data scientists found even more candidate sea feed stars, 655 in fact. They then sorted these into one of two classes, and found that 35 of these 655 stars were classical sea-feeds, the younger of the two. This was really exciting, especially since the Galactic Bulge was thought to contain mostly elderly stars that are at least 8 billion years old. Recording their pulsation periods, the team revealed that all 35 of these sea-feeds were less than 100 million years old, and some of them may be as young as 25 million years old. To put that in context, our own son is about 1,000. 4.5 billion years old, so the youngest sea feed has only been around for 0.6% of our sun's lifespan.

The team's exploration of sea feeds culminated in another major discovery. By mapping the 35 classical sea feeds they found, the team was able to trace a completely new feature in the Milky Way, a thin disk of young stars that stretches right across the galactic bulge. Buried behind thick clouds, It had remained unknown in all previous surveys of the region. In revealing this structure, combined with the discovery of all the sea feeds, as I mentioned earlier, scientists have inferred that there has been continuous star formation along the midplane of the galaxy for the past 100 million years. There might also be even younger sea feeds that we haven't seen yet, as these stars would be so bright that they would be saturated in the VVV survey.

The fact that we found this thin disk of young stars within the galactic bulge is incredible. We used to think that the galactic bulge was an ancient feature of our galaxy's past, where exclusively old stars had formed separately from the stellar disk. But this finding reveals that things aren't so black and white, and that the formation of newer stars within the bulge could be a natural progression of our galaxy. But, even more inspiring perhaps, is a discovery by the Vista Infrared Survey that lies at the ancient heart of our Milky Way galaxy. In 2016, for the first time, a type of ancient star known as R.R. Lairay, another variable

star was discovered in the center of the Milky Way galaxy by a team led by astrophysicist Dante Meneti and Rodrigo Contreras Ramos. This type of star is usually found in globular clusters, which tend to orbit the outer regions of the galaxy. A globular cluster is a tightly packed group of stars that contains tens of thousands to millions of stars bound together by gravity. They're also really ancient, containing a stellar population that can be over 10 billion years old. The team found 12 R.R. Lairay stars during the VV. V survey, which suggests that they might be the remnants of an ancient globular cluster right at the heart of our galaxy.

This finding also provides evidence that might help astronomers to decide between the two competing theories of how nuclear bulges form. While some scientists think that the nuclear bulge forms early in the galaxy's evolution, when multiple smaller galaxies violently collide, others say that it forms gradually over time, where gas is funneled inwards to trigger star formation. Finding these ancient stars here suggest that the bulging center of the Milky Way likely grew through the merging of primordial globular clusters, therefore supporting the first theory. So not only does it hint at our own galaxy's beginnings, but it also offers compelling

evidence into how these galactic bulges might form in other similar galaxies. Speaking of ancient stars, Vista was able to find two new globular clusters as part of the infrared survey in 2011. In this visible light image, a known globular cluster, U.K.S. 1, can be seen on the right as a hazy red splotch. This cluster had been the dimest known globular cluster until the new discoveries. Now, compare this same patch of sky, but this time in Vistas infrared light. Suddenly we can see what we have been missing.

Much more faint than the known U.K.S. 1, we can make out a second globular cluster, this time in the upper left of the image, which has been named VVV-Cl001. Another globular cluster, aptly named VVV-Cl002, was found soon after. And this small, faint group of stars may be the closest known globular cluster to the center of the Milky Way. Did you know that there were only 158 known globular clusters in the Milky Way before these new ones were found by Vista? For the survey to identify two more of these rare stellar objects is quite a significant

accomplishment. Within this central region of the galaxy, it's easy for younger stars and cosmic dust to obscure globular clusters, especially since their age prevents them from shining as brightly. But now that they've been revealed, these features bring exciting possibilities for further study. It could just be an illusion of perspective, but scientists have wondered whether VVV-Cl 001 is gravitationally bound to U.K.S. 1. If this is the case, then they would be the Milky Way's first known binary globular cluster.

the pair. We found binary clusters in other galaxies, like in Centaurus A and the Large Magellanic Cloud, but scientists think it might be when these gravitationally bound clusters collide that we get the most massive globular clusters, like Omega Centauri. So studying a binary cluster right in our own galaxy could produce some amazing insights into this process. It's all speculation at the moment. But it's definitely cool to think about.

In addition to globular clusters, the Vista Infrared Survey identified a multitude of other types of star clusters. At least 96 new open or galactic clusters have been found, which typically contain fewer, younger stars and are much more common than the globular type. Like the globular clusters, they have been hidden by cosmic dust, but Vista's 4.1-meter infrared telescope has lifted the curtain to show them in all their glory. Take a look at just a few of these stunning images we now have of these objects. One of these open clusters, VVVVCL003, is much more difficult to make out in images compared

to the tightly packed globular clusters. Try and see the density differences in the stars in this section of the image compared to the surrounding regions. It was found by Vista 15,000 light years beyond the Milky Way center, and also happens to be the first of its kind to be discovered on the far side of the galaxy. Vista's infrared observations have unveiled dozens of hidden star clusters and millions of previously unseen stars. They have revealed new stellar nurseries where stars are born, and they have broadened

our understanding of the formation of our Milky Way. at the sky through different wavelengths has brought about a new era of galactic exploration, and I can't wait to see what else astronomers and data scientists are going to uncover thanks to Vista's 3D map. As we continue our exploration of our Milky Way galaxy through the lenses of these incredible telescopes, there is one feature you almost certainly want to know more about that we've not fully touched on yet, those spiral arms. Once again, there are surprising mysteries surrounding such central features of our galaxy structure.

We've all seen pictures of galaxies, often glorious objects with spectacular colours and shapes. However, because they are static images, it may make you wonder how they rotate. The first obvious thought is that they spin around an axis, perhaps looking something like this as they do so. Would it surprise you to hear that this is totally wrong? Galaxies are not solid objects, but rather made up of millions to trillions of stars. Each star follows their own orbit, although they are often going in the same direction at least. But actually, one of the main reasons a spiral galaxy, such as our Milky Way, does not orbit

like the first example, is that angular momentum would wind the arms up into tighter and tighter spirals. We don't see this, so something else is at play. The leading theory is that these arms are caused by density waves, meaning a galaxy's rotation would in fact look like this. Here, the arms stay in place, or at least move extremely slowly, as stars and gas pass through them. Another theory is that shock waves produced by supernova and stellar winds are the cause of the arms. These theories might not be mutually exclusive, And both processes may be at work here. Density waves are potentially caused by the self-gravity of stars as they orbit after they

have been perturbed by another force. As stars have a gravitational influence on each other, eventually a pattern forms where their orbits meet around certain areas in the galaxy. Very, very interestingly, density waves are even seen in certain parts of Saturn's rings. Here you have a section of ring that appears like the inside of a tree trunk, but this is not the case. In this region, the ring is influenced by the gravity of small shepherd moons tucked inside the rings.

What you are actually looking at is one very tightly wound ring, a bit like an LP record. And just like with a galaxy, this arm stays the same shape, never getting tighter or looser. Between these arms is where the majority of star formation takes place in a spiral galaxy. The gas and dust within a galaxy clump up in these arms too, which is why you often see star form in nebula dotting the arms. The arms are also brighter, not just because there are more stars here, but also because all the hot, young, bright stars are found in these regions. Because the hottest types of stars are so short-lived, by the time they move away from the

arms, a lot of them will have already burned out. Another interesting phenomenon to do with spiral galaxies is something caused by dark matter. In the early universe, when dark matter was more dispersed, stars within galaxies that are dominated by normal matter would orbit a lot slower around the outside of the galaxy than towards the center. However, today, stars are moving a lot faster near the edge of the galaxy, thanks to the influence of dark matter. Dark matter, both in our Milky Way and beyond, is mysterious in that it cannot be seen

or observed in any way other than by its gravitational influence. Dark matter seems to have clumped towards the center of galaxies over time, making stars orbit faster than they should, around the edge of a galaxy, if only gravity from normal matter was accounted for. Other theories also exist about why this may take place, but these would have to change the way we currently understand physics. Anyway, how do we know about this change in the way stars orbit galaxies? Well, of course, we can see back in time when we look at extremely distant objects.

Stars within galaxies billions of light years away seem to orbit slower than stars much closer to us, and this effect scales depending on the distance to the galaxy. Of course, though, there are some rule breakers out there. exceptions to the rule that our Milky Way galaxy seems to follow. While most galaxies have stars that orbit like this, a few have been spotted that have leading outer arms. One example is NGC-4622, a bizarre galaxy that rotates in the direction the arms are pointing. This was hard to accept at first until smaller inner arms were also found.

This unusual galaxy has probably experienced a merger in its not too distant past, which likely caused this phenomenon. Another rule breaker is the Black Eye galaxy, which has two counter-rotating disks of gas and dust. The inner disk, where you can see all the dust lanes, rotates normally, whereas gas in this outer disk, rotates the opposite direction. Interestingly, stars in this outer region do not seem to be orbiting retrograde, meaning it is just the gas that does so. It is believed that gas must be still getting fed into the galaxy

from the intergalactic medium, or that this galaxy also merged with another extremely gas-rich galaxy. So while our Milky Way rotates in a counterclockwise direction, it did not necessarily need to do so. With a different set of events in its past, it could have rotated the opposite way entirely. Apparently, the galaxies at 8 were not enough disruption. to bring this about. Speaking of disruption, external collisions from neighboring galaxies are not the only hiccups our galaxy has had to contend with. It is more than capable of creating disruption on his own, like the time a cluster of

supernovae went off in quick succession in one of its arms. Hear that? It's your money calling. It wants a promotion. Elevate your savings with the Scotia high-interest savings account. Always earn high regular interest rates that grow the more you save and invest. Conditions apply. Visit scotiabank.com slash h-I-SA to learn more.

Scotia Bank. You're richer than you think. When 15 supernovae go off close together, both in time and proximity, it makes quite a bang. It should be of no surprise that such a violent event should fundamentally transform the region of space around where it occurred, Interstellar dust was swept aside from the forces of those concurrent blasts, creating a monumental void of low density matter, and a shockwave that continues to hurtle across the galaxy to this day at a rate of 6 km a second. In its wake, plasma, reaching 1 million degrees Celsius in temperature.

This simultaneous Swiss cheesing and heating up of the interstellar medium. is what is now called a hot bubble and represents both the end of stars and their beginning. But this is not some distant structure that lurks in a faraway corner of the Milky Way. Our solar system is in it, charging for its point of origin head first. Welcome to our local hot bubble. What scientists now realize is the local environment that exists around our solar system. It is a neighborhood we are still exploring, but its nature is becoming clearer and clearer. So what do we know about the local hot bubble? How did it form? And what more is there to be discovered?

The local hot bubble was not always something we knew about. First identified in the 1970s from observations of low-energy x-ray emissions that were detected over the entire sky, the local hot bubble was hypothesized to be a large cavity in the interstellar medium, called a super bubble filled with tenuous, million-degree, low-density gas. In the 1990s, scientists found that X-ray emissions could happen anywhere neutral atoms interacted with the solar wind, challenging the idea that the emissions must point to a large hot bubble. But soon, evidence would reveal that the hypothesis,

synthesis from decades earlier was indeed correct. In 2014, NASA confirmed the existence of the LHB through the diffuse X-ray emission from the local galaxy mission, known as DXL. While soft background radiation can come from other sources, like from comets, for example, the mission found that only 40% of the fog of low-energy x-rays came from within our solar system. This affirmed that the dominant source was diffuse X-ray emissions emanating from the million-degree region of interstellar plasma, known as the LHB. Although this confirmed the bubble, questions remained about what could create such

a massive void, and what might explain the thousands of surrounding young stars. The prevailing answer proved to be both violent and fascinating. Recent research suggests that the local hot bubble was the aftermath of around 15 supernova explosions that occurred sequentially within a span of a few million years, erupting in relatively close proximity to one another. Scientists estimated that the first of these massive stellar explosions went off roughly 14 million years ago, each expelling enormous amounts of energy, pushing out the surrounding interstellar material and heating the remaining gas to extreme temperatures. Evidence of these ancient explosions has been preserved in our Earth's geological record in deep sea sediment deposits,

in the form of a special isotope called IN60. This radioactive isotope can come from a few different sources, but the most common source of iron 60 is believed to be supernova explosions. We know that the source of the isotope is extraterrestrial because the Earth itself has no way of producing iron 60 on its own, and matching deposits have been found on the moon as well. The reason that this radioactive isotope is special is because we know how long its half-life is. We know that it decays into Cobalt 60, another radioactive isotope, before it finally decays into nickel 60, a stable element.

Iron 60 has a half-life of 2.6 million years, and cobalt 60 has a fairly short half-life of just 5.3 years. Because of this, when we find a deposit that contains these elements, scientists can compare the amounts of iron 60, cobalt 60 and nickel 60, like an elemental clock to reveal when that material was deposited on our planet. Luckily for us, international research teams have found several such deposits over the last couple of decades. In 2016, iron 60 deposits were found in deep sea cross samples taken from the Pacific, Indian,

and Atlantic oceans, indicating two distinct spikes in the radioactive debris that pointed to several supernova events in the not-so-distant past, and not too far from our solar system. 326 light years away. The sample showed a spike of iron 60 between 3.2 and 1.7 million years ago, and another spike between 6.5 and 8.7 million years ago. Nuclear physicist Anton Walner, who led one of these research teams studying the deposits, said that the fact that the more recent debris was spread across 1.5 million years, suggest that there were a series of supernovae that occurred one after another in close succession.

Astrophysicist Dieter Breitchbert, who led a second team of scientists, identified a likely source of these supernova explosions, which would have occurred 196 to 423 light years from the sun. These supernovae that created our local hot bubble may have been part of an aging star cluster, surviving members are now associated with the Scorpius Centaurus stellar group. Using the iron 60 deposits, the team was able to trace the signals of two supernovae, one that happened 1.5 million years ago and the other 2.3 million years ago, as the result of the deaths of stars that were 8.8 times and 9.2 times the mass of our sun, respectively. In fact, our LHB is still

growing today, albeit much more slowly than when the supernova exploded millions of years ago. The speed of expansion has plateaued at about 6 kilometers per second now, according to astrophysicist Catherine Zucker. In 2022, Zucker authored a groundbreaking paper that reconstructed the evolution of our galactic neighborhood, tracing the chain of events that created our local hot bubble, and led to the formation of all the young stars we see nearby today. From there, they made an incredible discovery. Using data from our old, faithful guide telescope, Zucker and her team were able to construct a 3D spacetime map, showing that within 500 light years of our planet, all of the young

stars and star forming regions reside on the surface of our local hot bubble. With these 3D positions and the 3D motions of the stellar clusters, they traced back 20 million years of star formation history near our local hot bubble. The implications were clear that all of the well-known star forming regions near our solar system had formed along the outer edge of the local bubble as it swept up gas during its expansion. From the local hot bubble's birth 14 million years ago, Zucker and her colleagues identified four epochs of star formation on the bubble shell. Starting about 16 million years ago, we see the birth of the upper Centaurus Lupus, or the

UCL star cluster, followed by the lower Centaurus Crux, or LCC star cluster. These formed about 49 light years apart from one another, and about 14 million years ago, these stellar populations were the source of the stars that went supernova to create our local bubble. About 10 million years ago, we see the first of the four star-forming epochs after the formation of the LHB, the Upper Scorpius Association and older of the Eucca stellar populations are born in the first epoch. Six million years ago, the second star-forming epoch formed Crona Australis and the older

stars of Taurus. Then around two million years ago, the stars in Lupus. and Chameleon, as well as younger stellar populations of Taurus and Ophiuchus, came to be in the third epoch, and finally, our present time falls within the fourth star-forming epoch. We can observe the dense star-forming molecular gas that surrounds the LHB, which will eventually lead to more star clusters being born along the bubble's outer edge. With all of this stellar creation, You might be surprised to learn that we are interlopers. Our sun did not form inside the local bubble.

In fact, the sun was about 978 light years away when the first supernova went off in UCL and LCC, only joining up with the LHB about 5 million years ago as its path through the galaxy took it into the bubble. With the trajectory shown in yellow dots, you can see our son's location just before it entered the bubble. And now, just by coincidence, our sun happens to be located near the centre of the LHB. Drifting into the heart of what was once a raging furnace,

scientists became interested in mapping out the ongoing temperature within the local bubble. You might wonder why we're so calm, if temperatures of plasma here can reach 1 million degrees Celsius. The key lies in that plasma's density. Look, this 3D map from Zucker's 22 publication shows our local hot bubble in dark blue. The density inside our bubble is extraordinarily low, containing about 100 times less hydrogen than the typical interstellar medium. So, while the temperature of this gas soars to around 1 million degrees Kelvin, giving rise to the diffuse x-ray emissions we have observed around the whole sky, we don't have much to worry about. Tracking temperatures within the local bubble has provided more evidence of its existence.

The extended Rotogen survey with an imaging telescope array, better known as the E-Rosita X-ray telescope, has been able to gather the most detailed all-sky survey of soft X-rays to date. And that data has been used to map the LHB and our solar neighbourhood in much more. more detail than before. Launched aboard the joint Russian and German mission, Spectrum Renzhen Gamma, or Spectre, RG, in 2019, data from the E-Rozeta X-ray telescope has allowed a team of scientists led by the Max Planck Institute for Extraterrestrial Physics to create a 3D map of the

LHB and identify a temperature gradient where the Galactic South was slightly hotter than the galactic north. This temperature dichotomy could be explained by supernova explosions in the past few million years. And by creating this bubble map, the team also found that the LHB is stretched out towards the poles of the galactic hemisphere. This is because the hot gas in the bubble expands out in the direction with the least resistance, which happens to be away from the Milky Way's Galactic Disc. Along with identifying temperature variations and the shape of the bubble, the team compiled

this and other data to create an even more detailed map of our galactic neighborhood. In the new 3D map, our local hot bubble looks like a three-dimensional splatter surrounded by and even overlapping other galactic structures. These other structures represent known supernova remnants like the GUM nebula shown here in red, and dense molecular clouds, shown here in orange. With the new data and 3D maps, these super bubbles seem likely to be common in our galaxy, meaning our Milky Way is a galaxy that's sort of like Swiss cheese. The cavities of our Swiss cheese galaxy are blasted out by gigantic supernova explosions,

with new stars forming along the edges of the holes created by dying stars. And like Swiss cheese, it appears that some of these super bubbles may have tunnels connecting them to other bubbles or other structures, suggesting our local hot bubble could be part of an intricate network of similar features throughout our galaxy. For example, we have the Canis Majoris Tunnel, which lies on the Milky Way's Galactic Disc, and is believed to connect our local hot bubble to the Gum Nebula or another larger nearby by Superbubble. But the 3D map also revealed another, previously unknown interstellar tunnel, stretching towards

the constellation Centaurus, possibly connecting our local bubble to the neighboring Loop 1 Superbubble. While these interstellar tunnels are tantalizing, our current understanding of them is limited. Nevertheless, these tunnels of hot gas and bubbles of star formation shaped by the interstellar. the death of gigantic older stars has me in awe of how powerful and interconnected the evolution of our local galactic neighborhood really is. It suggests that stars are not just born and die in isolation, but that their energetic output continues to mould the environment for millions of years after their demise. And as our observational tools become more sophisticated, we are beginning

to uncover the extent of these hidden structures. We are getting towards the end of our tour of the Milky Way galaxy. But speaking of hidden structures, I have been saving one of the best examples of those out my sleeve until now. Something jaw-droppingly massive, lurking invisibly and yet towering above us all. Something that I can guarantee will mean you never look at the Milky Way the same way again. You're that? It's your money calling. It wants a promotion. Elevate your savings with the Scotia high-interest savings account.

Always earn high regular interest rates that grow the more you save and invest. Conditions apply. Visit Scotiabank.com slash h-I-SA to learn more. Scotia Bank. You're richer than you think. As mentioned already, the center of the Milky Way is a difficult place to image. Density, temperature, and turbulent velocity, a measure of chaotic fluid motion, are around 1 to 2 orders of magnitude higher here than anywhere else in the galaxy. The cosmic ray energy density, a proxy for energetic activity, is 2 to 3 orders of magnitude higher.

This region is home to vast complexes of molecular gas, about 20 million. in solar masses worth, dense cosmic clouds, ionized plasmas, extreme cosmic ray energy, ultraviolet and x-ray radiation, and turbulent magnetic fields. It is a hotbed of cosmic activity from the formation of stars to exploding supernovae. And let's not forget Sagittarius A. Star, the supermassive black hole four million times the mass of our sun, at the very center of its wall. These conditions are hugely exciting for astronomers, but they make the galactic center notoriously hard to study. Visible light can't penetrate the dense clouds of dust and gas.

So as we saw with Vista, researchers turned to other parts of the electromagnetic spectrum to lift a veil and reveal the secrets at the heart of the galaxy. However, Vista's infrared viewpoint is not the only way to look at this chaotic region. The waves have the longest wavelengths of the electromagnetic spectrum, from a few millimeters to hundreds of kilometers, and the wavelengths in the range of millimeters to tens of meters are ideal for radio astronomy. They pass through the obscuring clouds of gas and dust, giving us a clear view of what lies beneath.

In the early 1980s, Fahad Yusif Zadeh, studying for his PhD, was using the very large array telescope in New Mexico to produce a radio map of a section of the galactic center. He was planning to study star-forming regions, but narrow strips of radio emission were streaking across the entire survey area right through the parts he was interested in. He thought they must be artifacts in the data, or imaging errors, which any scientist will tell you is highly annoying. So after much frustration and no luck resolving the problematic artifacts, he returned to the VLA to image again at another frequency.

And that was when his Eureka moment struck. At 4 a.m. one morning, he was comparing the two samples taken at different times using different wavelengths, and he saw the same structures in both images. This was no artifact. This was a very real finding, something unlike anything he, or anyone else for that matter, had come across before. Zadee was seeing highly ordered structures where previously only chaos was thought to exist, and they had some very unusual features.

Most striking was their vast scale. These were continuous, narrow strips of radio emission, 50 to 1. 100 light-years long, but only 1 to 3 light-years wide, dangling vertically above and below the central molecular zone, the most extreme part of the Milky Way. Some appeared in pairs or clusters running parallel to each other like strings on a harp, each separated by a standard distance of around one astronomical unit, the distance between Earth and the Sun. When he cross-checked them with the infrared data from that area, Zarday also discovered they had no counterpart in that area of the spectrum. This told him they were non-thermal emissions, that is to say, they were not

produced by heated gases. This was cooperated by other measurements such as spectral index and polarization, which showed that the filaments were highly magnetic and emitting synchrotron radiation. Synchrotron radiation occurs when electrons moving near the speed of light interact with a strong magnetic field, which beg the question, what on Earth, or should I say, not on Earth, was accelerating the electrons to such speeds? The emissions along the length of the structures were continuous, ruling out localized events like star formation or supernova remnants. So Zadee dubbed them not non-thermal filaments and suggested they were likely related to galactic scale phenomena.

His observations didn't correspond to anything else in the known galaxy, and Zadeh had many more questions. Where did the non-thermal filaments come from? What was maintaining their linear structures over such vast distances of space and time? Why, when clustered, were they so evenly spaced? But almost as soon as this startling discovery was made, the trail started to go cold. The available telescopes at the time simply didn't have the sensitivity needed to provide answers. Over the next 35 years, only a handful of other vertical non-thermal filaments were revealed and categorized. Some were even given enigmatic names like the snake, pelican and bent harp.

Sadly, there wasn't enough data to make any great leaps forward in understanding. Well, not until 2022, and MIRCAT's mind-blowing image. Our third incredible telescope. The MIRCAT Radio Telescope at the South Africa Radio Astronomy Observatory, or Zara-O, is comprised of 64 interlinked antennas, each with a 13.5-meter parabolic dish, spread over 8 kilometers of radio silent zone. Built over 4 years, the full array was inaugurated in 2018. Its location in the Southern Hemisphere is perfect for imaging the center of the Milky Way, thanks to our sun's axle tilt relative to its own position in the galaxy.

So, Mierkat has a direct line of sight into the CMZ and the galactic center. Over the course of three years, an international team led by Dr. Ian Hayward, and including Zade, now professor at Northwestern University, directed me a cat to a 6.5 square degree portion of the galaxy, a section of the sky around 30 full moons wide, with Sagittarius A-star right in the middle. Using L-band radio frequencies of 856 to 1,000, 712 megahertz, equivalent to wavelengths of 18 to 35 cm, they split this area into a 20-part mosaic, directing the telescope to survey each tile in turn over a total of 144 hours on target.

This was the first time Meerkat's full array was used, with 60 to 62 dishes sampling the sky at any one time. After generating 70 terabytes of raw data, not quite as much as Vista, but still the equivalent to 700 hours of 4K YouTube content, the team then had to process it. That was no mean feat. Given the complexity of the environment, they needed to put the data through a high-pass filter using a method called Difference of Gaussians. This is a commonly used edge smoothing technique to remove background.

noise and enhance the visibility of fine structures especially important for visualizing non-thermal filaments. And this is the result. More like a work of art than a scientific study, it captures a wealth of features. Some are well known, like Sagittarius A-star seen in the central saturated area here, and clearer views of previously known supernova remnants and star-forming regions. This here is a supernova remnant. To its left is a runway pulsar, the mouse, and up on the right, one of the longest and most famous non-thermal filaments, the snake. As noted by the team, one of the most startling discoveries was the sheer number of filaments

apparent in the image, an order of magnitude greater than all previously known, most of which had never been seen before. This was game-changing for Zade and his colleagues. Now we finally see the big picture. A panoramic view filled with an abundance of filaments, he said. This is a watershed in furthering our understanding of these structures. There was finally enough data to carry out meaningful population studies. They set to work carrying out statistical analysis of the filaments.

This work, published in the astrophysical journal letters, not only further categorizes the filaments, but gives tantalizing clues to their origin. The new data confirmed that all of them are magnetized. In fact, the team found that the magnetic field was significantly greater, in some cases up to 10 to 100 times stronger than typical galactic magnetic fields. The new analysis also confirmed that synchrotron radiation, is a defining characteristic. Interestingly, the mere cat data revealed that there is a steepening with galactic latitude.

In other words, the filaments appear to cool as they stretch away from the galactic plane. This gives us a clue as to their possible origin. The electrons further away from the galactic plane could be older, implying that the filaments are related to past activity of Sagittarius. a star. And there was another clue that suggested this two, enormous structures known as radio bubbles. First discovered by Hayward, Zadeh, and the Mirkat team in 2019, these huge radio-emitting structures stretch symmetrically above and below the galactic plane, forming an hourglass shape thousands of light years across. They are thought to have been created by a phenomenal output.

from Sagittarius A-star, about 100,000 to a million years ago. An event, powerful enough to leave such a scar on the galaxy, could have been vast quantities of gas and dust falling into the black hole, or a huge and sudden burst in star formation close by. An incident like this would have triggered an intense outburst of energy and whipped up galactic winds driving gas in cosmic rays violently away from the galactic center, stretching and amplifying magnetic field lines in its wake,

creating those bubbles and non-thermal filaments. What's more, strong magnetic fields, which, as we now know, are a confirmed characteristic of all filaments, capture cosmic rays. And the great thing is, we can date them. Those detected in the filaments by Amirat match the proposed period of the Sagittarius A-star outburst considered responsible for the radio bubbles. In other words, they are the same age. The position and capabilities of Mirat, alongside the same high-pass filtering used to resolve the non-thermal radio filaments, not only revealed these bubbles in astonishing detail, but showed almost all of the filaments are confined within them. This close physical association adds

even more weight to the argument that the same energetic event created them. Something powerful enough to create the bubbles would certainly be able to accelerate electrons to near the speed of light, with the stretch magnetic field lines channeling them to produce the filament's signature synchrotron emission. With this hypothesis in mind, Zaday and the team described the formation of non-thermal filaments as magnetized streamers in a cosmic ray-driven wind. It certainly paints a compelling picture for the possible origin of the filaments, but it is by no means conclusive, as even the authors themselves attest. Other theories are being worked on. With a mystery this tantalizing, other astronomers have been studying the filaments too, but this single image is still the

one that's told us the most. Zadar wasn't kidding when he said it was a watershed moment, But with so many unanswered questions, some going back 40 years, where does that leave us? Are non-thermal radio filaments merely a galactic curiosity? Not by any means. They are a riddle wrapped in a mystery inside an enigma, and could shed light on one of the biggest unanswered questions out there, how supermassive black holes regulate star formation within a galaxy. Scientists know that the active centres of galaxies must transfer energy and matter into interstellar space through a process called galactic feedback.

If they didn't, star formation would run away unchecked, using up a galaxy's gas and dust faster than observations tell us. But how this feedback happens is unknown. Mierkatt's detailed imagery of non-thermal filaments and the radio bubbles provides us with compelling evidence that this outflow of energy could happen in discreetly. great, but powerful outbursts. And this is something that has never been seen before. Fermi bubbles, discovered by NASA's Fermi gamma-ray telescope in 2010, are even bigger, hourglass-shaped configurations spanning a total of 50,000 light years.

These mind-bogglingly massive structures, colored magenta in this image, are thought to be millions of years old, likely caused by a violent outburst from Sagittarius A-star. which calculation suggests had the energy of 100,000 supernovae. This is much more powerful and ancient than the event proposed to have made the filaments and radio bubbles, but together they paint a picture of intermittent outbursts from deep within the heart of our galaxy. Both have the potential to regulate star formation, ensuring that the Milky Way doesn't suffer from burnout. As scientists continue to unravel the mystery, of non-thermal filaments and tackle the big questions about how the universe works,

the trail doesn't seem to be going cold again anytime soon. Since the first full-array image, Meerkat has found more of these mystery strands in other galaxies with very similar properties to the ones we see in the Milky Way. Their very existence elsewhere suggests a common underlying mechanism that alludes to their role in fundamental galactic processes. To conclusively piece together the whole picture will require another step change in imaging resolution. And hopefully that's not too far off, as Mirat, already awarded by the Royal Astronomical Society for its spectacular observations in radio astronomy, was built with longer-term goals

in mind, namely to be incorporated into the square kilometre array. With a total collecting area of one square kilometer, it will be 50 times more sensitive than any other radio instrument in existence, and it's expected to be fully constructed by 2028. Keeping an eye on developments in other parts of the electromagnetic spectrum will be important, too. Zarder believes that the next breakthrough will come from gamma-ray telescopes. Imaging at higher frequencies results in higher resolution imagery, which has potential to show us whether the filaments, the radio bubbles that contain them, and the vast Fermi bubbles are connected. and elegance in order rising out of chaos, and observing non-thermal filaments streaming out

through the cosmic winds certainly fits that notion. A tour of the Milky Way galaxy could go on and on, but there is one last feature I want to explore on this journey of our often misunderstood home, the shining jewels in the Milky Way's crown, and I mean that shining part quite literally. But to understand it, we must first look further afield. Hear that? It's your money calling. It wants a promotion. Elevate your savings with the Scotia high-interest savings account.

Always earn high regular interest rates that grow the more you save and invest. Conditions apply. Visit scotiabank.com slash h-I-SA to learn more. Scotia Bank, you're richer than you think. Have a look at this beautiful image captured by the James Webb Space Telescope. Immediately, you'll notice two types of objects. First you'll see the nearby stars within our own Milky Way galaxy, which look like points of light surrounded by diffraction spikes. But further in the background, you'll see entirely new galaxies, each containing billions of stars smeared out into elliptical or spiraling blurs.

What you probably won't see are distinct individual objects within those other galaxies, as they are far too distant and blend in with. all the other sources of light. But there is one exception to that rule. One type of object that is so bright you can make it out from billions of light years away, so bright that it stands out from all the surrounding stars in its galaxy, a quasar. But what if I told you that a whole bunch of tiny quasars were hiding in plain sight right within our own Milky Way? How can that be when And they are some of the brightest objects in the universe. Don't worry, you're about to find out. Astronomers have been pointing their telescopes up at the night sky for centuries.

Yet, it was only in the 1950s that they set out on a quest to map out what the universe around us looked like in radio waves rather than visible light. Think of this as the astronomer's version of putting on night vision goggles. At first, they didn't see anything out of the ordinary. Many of the same galaxies that emitted visible light also emitted radio waves, so they could be seen with or without the goggles. But then, among the stars and galaxies that were known to populate the night sky, astronomers saw something new, something that shone very brightly in radio waves, but had never before

been seen in visible light. And there wasn't just one of these objects. By 1960, observations quickly grew until hundreds of mysterious radio sources had been recorded across our sky. At the time, astronomers didn't have a clue what the origin of these radio waves could be. For all they knew, the waves could come from a giant intergalactic network of alien radios. But what they did learn from follow-up observations using more precise telescopes like the Hale telescope is that you could see these objects in the visible part of the spectrum.

They were just extremely small and faint. They were far too small to be galaxies. They appeared as points, not smeared out blobs in the sky. But they also couldn't be regular stars, because regular stars don't typically emit much energy at all in radio waves. For this reason, these mysterious objects came to be known as quasi-stellar radio sources, which quite literally translates to something like a star, but not a star. a star that emits a lot of radio waves. That name eventually got short into something that was a

little bit more palatable, quasars. Even with the catchy name, it took astronomers and physicists nearly 30 years to really pin down what these quasars were. And unfortunately, it's probably not alien radios, although the real answer is still extremely fascinating. It turns out that the explanation centers around black holes, and not just, ordinary black holes, but supermassive black holes that can be millions or even billions of times the mass of the sun. Such supermassive black holes are frequently found at the center of large galaxies, and although black holes can't emit any light themselves, they can make quite the spectacle out of the accretion disks orbiting around them. If you want all the details,

you can queue up our older video on quasars here, but for now let me just give you a quick Summary. Matter orbiting a black hole can spiral inward as it loses energy due to internal friction. Much of that energy ultimately gets converted into light that streams outward from the black hole. But in some cases, the accretion disk also splits out relativistic jets of ionized matter, culminated by powerful magnetic fields along with the spin of the black hole and its surroundings. The particles in these jets can propagate through the universe from galaxy's to galaxy as cosmic rays, sending out radio signals as they're pushed around by intergalactic

magnetic fields. Overall, quasars emit so much energy that a single quasar in a distant galaxy will outshine the other hundreds of billions of stars in that galaxy combined. That's why, when quasars were first observed, they appeared as small as a star, but far brighter than any star outside of the Milky Way could have ever been. Now, the Milky Way has its own supermassive black hole right in its center too called Sagittarius A-star. But for better or for worse, the accretion disk around our black hole is too thin and faint to call it anything close to a quasar, and until something dramatic happens, Sagittarius A-star will likely remain calm and mellow. On one hand, we're kind of lucky, because a quasar that close to it,

Earth would emit enough high energy radiation to be potentially fatal to terrestrial life, which makes you wonder about the kinds of life that could arise in galaxies that do contain quasars. But on the other hand, we're missing out on a second source of light in the sky, illuminating our planet almost as brightly as the sun, and it would be so cool to get to study a quasar from up close. So can you imagine my surprise when I learned that we might actually have the best? of both worlds. Quasars, alive and active in the Milky Way, and yet not so powerful as to wipe out

our entire biosphere. How could this be possible? If the one supermassive black hole at the center of our galaxy isn't a quasar, then where could they be? It took a couple of decades, but scientists eventually discovered that quasars can form around ordinary black holes too, not just supermassive ones. These ordinary black holes, just a few times more massive than the sun, typically form when giant stars collapse, so there are loads of them spread throughout practically any galaxy. You probably wouldn't expect one of these black holes to have its own accretion disk, but once in a while, a nearby orbiting star might get sucked into its gravitational pull and act as a source for the smaller, less deadly version of a quasar. A might be a might

microquasar. Even though the jets of a microquasar are much weaker, they can be easier to study because of their proximity to Earth, allowing us to learn more details about the properties and dynamics of both microquasars and their larger, full-scale counterparts. The very first microquazars was discovered in 1979, and was given the obvious name SS-433, it was originally documented as the 4333rd entry in a catalogue of stars compiled by astronomer's Nicholas Sandelike and Bruce Stevenson two years prior. To date, only a handful of microquazars have ever been found, and SS433 in particular

has been a subject of widespread wonder and research. Despite its name, SS433 is more than just some ordinary star in a catalogue. It is a Type A super giant orbiting around a stellar mass black hole in a binary system. As the black hole accretes material from the super giant star, it produces a pair of jets perpendicular to the line of sight from Earth, meaning that the jets themselves will never actually hit us or reach our detectors. But as the jets propagate outward, they emit light in all sorts of directions, allowing us to image them at various wavelengths and learn more about how they are.

are produced. One of the first things we saw was that there are actually two types of jets emanating from SS433. The inner jets extend out just a couple of light years from the black hole before fading away, while the outer jets appear 75 light years out and span an additional 300 light years or so. We still don't know how exactly these outer jets form, or why they terminate after 300 light years. And we only have a right. rough idea of what they're even made of, but a recent study from the Hess collaboration gave us some new clues to answer these questions. One such clue is the presence and distribution of high-energy photons called gamma rays

being emitted by SS-433. Ordinarily, stars or accretion disk could not be expected to produce any gamma rays, because their temperatures are far too low. But the outer jets coming out of SS-433 seem to be expected to produce. to emit them in spades. What's even more surprising is that even though the outer jets are extremely hot, the spectrum of light that they're emitting isn't consistent with an ordinary thermal distribution of photons.

So what's generating all of those gamma rays? The current theory is that the outer jets contain high energy electrons that can bump into lower energy photons passing through the system, and they transfer their energies to the photons during those collisions. This process goes by the name of inverse compton scattering. The scientists at Hess realized that measuring the energy in these emitted gamma rays can give us a lot of information about the energy of the electrons in the jets that produced them in the first place, and what they found was in full support of the inverse Compton scattering

theory. The highest energy gamma rays, carrying over 10 terra electron volts of energy per photon, and or about 10 trillion times more energy than a photon of visible light, were primarily coming from the innermost region of the outer jets. Gamma rays with lower energies, on the other hand, came from correspondingly farther distances down the jets of S-433. This distribution is a clear indication that electrons farther down the jets have less energy to transfer to photons than electrons right at the beginning, or in other words, as the

electrons stream along the outer jets, they tend to lose energy over time, presumably due to their collisions with photons. But how did the electrons acquire such large energies to begin with? Models suggest that their initial launch velocity from the black hole was just about one quarter of the speed of light, but by the time they reached the outer jets, these high energy electrons appear to be moving its speeds greater than 99% the speed of light, multiplying their initial energies by a factor of $1 billion. The Hess Collaboration believes that this wild acceleration occurs due to a shockwave at the base of the outer jets

caused by complicated configurations of magnetic fields. Each time an electron interacts with the shock front, it gains a boost of speed as if it crossed a boost pad in Mario Kart. And due to the diffusion of electrons back and forth within the jet, some electrons can cross over this boost pad over and over and over again, like an infinite speed glitch. This process is called diffusive shock acceleration, and it may be responsible for amping up electrons to energies in the hundreds of terra electron volts, just enough to be able to reduce the high energy gamma rays observed by Hess. But shedding light on the production of photons within the outer jets of SS-433 is just

the beginning. Quasars scattered throughout the Milky Way can hold treasure troves of information about the inner workings of even the most massive quasars in the centre of distant galaxies. And now that we know to look for them, microquasars are less like hidden gems and more like beacons in the sky, posing for our astronomers to capture their beauty in an entire spectrum of photographs and revealing ever more shocking surprises. it. There is still so much for us to learn about our Milky Way galaxy. And yet, as our telescopes peer through its obscuring starscape, we find feature after feature that causes my jaw to drop.

There are so many wonders out there, ranging from its enigmatic arms to its star-shrouded core, to its cavities of supernova explosions and towering filaments. Its black holes and quasars and its myriads of stars that shine and gleam through the sky. I'm in awe of how much there is to see and how much there still could be out there waiting to be uncovered. Our Milky Way feels like it has so many more secrets to reveal. So what do you think is still out there? And what discoveries have been your favourite so far?

Let me know in the comments below. You may have noticed this video didn't have any sponsors, and that's because it was brought to you by our astromauts on Patreon. Consider joining our Patreon to keep these videos thriving even when they're sponsor-free. It's the reason we can research deep into the topics we love without cutting corners or chasing clicks. Every new astromnaut allows us to explore bigger ideas and make every upload even better than the last.

So if you've ever thought about being a bigger part of this channel, join the crew to power Astrum and keep space, curiosity alive.