We Found a Giant Structure In Space and We Don’t Know What It Is

Our planet is haunted. Now you might think that is an odd thing to claim for an astronomy channel. But there have been whispers among astronomers that something is out there. Ghostly spectres lurking in our orbital path. Entities that have eluded scientific detection for decades. Drifting in perfect balance between cosmic forces. One claimed to have captured faint images of these ethereal silhouettes, looming up to 9 times wider than Earth itself. Yet others have searched the same regions of space and found… nothing at all. For over six decades, astronomers have debated their existence. Are these mysterious entities merely elaborate optical illusions? something truly extraordinary hiding in plain sight? What celestial phenomenon could simultaneously be so large, yet remain so elusive? Is the Moon truly Earth's only companion in our journey around the Sun? I'm Alex McColgan, and you're watching Astrum. Today we're investigating one of astronomy's most enduring mysteries, the controversial ghost moons, that may be silently accompanying our planet through the cosmos. This ghost story begins in 1961, when Polish astronomer Kazimierz Kordolewski first spotted two diffuse patches of sky that kind of looked like clouds through a telescope, which were located suspiciously near the stable L4 and L5 Lagrange points of our Earth-Moon system. In case you aren't familiar with Lagrange points, let me quickly explain. Lagrange points are positions in space where the gravitational forces of two large bodies are balanced by the centripetal force required for a smaller object to move with them. This creates a sort of gravitational equilibrium that allows the smaller objects to maintain a position relative to the two larger bodies. Lagrange points were named after the Italian-French astronomer and mathematician Joseph Louis Lagrange, after he published a prize-winning paper about this phenomenon in 1772. While we're going to be talking about the Lagrange points present in our Earth-Moon system in this video, similar points exist for other two body systems, such as between the Earth and the Sun, or Jupiter and the Sun. In any two-body system, there are five spots where gravitational forces and orbital motion create these Lagrange points, and they're labelled L1 through L5. Three of these, L1, L2, and L3, are considered unstable. Small objects may be temporarily captured near these points, like the NASA ESA satellite SOHO at L1, or the James Webb Space Telescope at L2, but they have to make corrections to their altitude and course every 23 days to avoid drifting out of position. Objects in these unstable equilibrium points are balancing on a metaphorical knife's edge, and any slight push from the solar wind, radiation, or the moon's gravity will tip the balance. But L4 and L5, these positions are stable. Unlike the other Lagrange points, these each make equilateral triangles with the Earth and Moon, and are resistant to gravitational perturbations. Because of this, objects like asteroids and dust tend to accumulate in these areas, and that's where our story picks up. Kordilevsky's observation of these ghostly faint clouds in the L4 and L5 Lagrange points, originally named Liberation Clouds, but later known as Kordolevsky Dusk Clouds, ignited a scientific debate that has lasted for decades, one that is still going on to this day. Immediately following his observation, other astronomers, both professional and amateur, attempted to locate the supposed clouds, But for years, nobody else could find them. At the time, observational techniques were far less advanced than today. Many astronomers questioned whether these dust clouds were real, or merely optical illusions. After all, detecting such faint structures against the darkness of space was a challenging proposition. That scepticism persisted for years. Every now and then, an astronomer would catch a glimpse of a dust cloud in one Lagrange point or the other. and sometimes clouds would be visible in both locations. A few astronomers, including Kordolevsky himself, captured photographs of the clouds. But for years, the dust clouds appeared so faint in the photos that they could not be reproduced in newspapers. These photos aren't like photos we're used to either. Images of these dust clouds have to be taken using photometric techniques, which involves glass photographic plates with long exposure times to capture the faint lights of distant celestial objects. They aren't of Hubble telescope quality. They serve more to identify changes in light intensity, and this is what astronomers would use as evidence of the cloud's existence. In 1966, NASA organised an airborne observation mission from its Convair 990 jet laboratory, operating far from city lights at an altitude of 12,000 meters. The astronomers on those four NASA flights were able to identify Khodolevsky dust clouds in both the L4 and L5 Lagrange points, even managing to photograph the dust cloud at L5. The orbiting solar observatory OSO6 also observed the clouds in 1966, and subsequent work was published measuring their brightness and size. However, in 1976, another astronomer named Siegfried Röse at the Max Planck Institute for Astronomy used numerical simulations to show that conditions were unfavourable for dust to accumulate in the L4 area, and questioned whether or not these clouds actually existed. Most of the KDC sceptics believed that the gravitational perturbation of the Sun, solar wind, and other planets have too strong of a destabilising effect on the L4 and L5 Lagrange points for KDCs to be maintained. Additionally, radar studies of the clouds around this time had produced negative results, leading many to believe there was nothing of circumstance at the Lagrange points. These doubts were further reinforced in 1983, when observers using a 61cm telescope near Tucson, Arizona, found no such clouds in either L4 or L5. Yet, just a few years later, in 1989, the clouds were photographed again by astronomer Winiarski. From an astronomical observatory in the Bierstadt Mountains in Poland, and Winiarski observed the KDCs to be a few degrees in apparent diameter. These were also the first three colour photometric observations of the clouds, and they revealed that the clouds appeared much redder than the counterglow, which is the sunlight that gets scattered by the general dust particles in space. This observation suggested that the dust in the KDCs is significantly different in composition to the other local space dust, which begs the question, where are these aberrations coming from? But then, once again, the existence of KDCs was brought into question, when in 1991, the Japanese Heighton space probe did one loop around the L4 and L5 Lagrange points in an attempt to detect dust particles, but didn't manage to find any. However, astronomers say that this should not be taken as evidence against the dust clouds, as Highton was only able to do one loop around each Lagrange point, and if the clouds do exist, the dust was likely moving too slowly for it to be picked up by Highton's dust detectors. So, as you can see, the scientific debate that began in 1961 after Kordolevsky's initial observation is one that has continued through the decades. But now, scientists seem to have made a breakthrough. In 2018 and 2019, astronomer Judith Slisbalo and physicist Gabor Horvath and Andreas Barthe were able to present clear evidence of the L5KDC by examining how the dust creates patterns of scattered, polarised light. To do this, they used a type of photography called polarised imaging, which uses a series These are filters that can show light bouncing at specific angles. When light hits these dust particles, it scatters differently depending on the specific composition and arrangement of the particles, offering clues to the nature of the clouds. After collecting a series of images through various polarised filters, the scientists found that the patterns of polarised light in the images matched theoretical predictions for what we would expect to see from sunlight that was scattered by dust clouds. What's more, in their 2018 paper on the observations, they said that, in fact, these results meant that the scatters cannot be anything other than dust particles. To back up these observations, they were able to further understand the formation of the clouds at L5 through the use of computer simulations. They calculated the motion of 1.86 million dust particles to see how dust in that region of space might behave, and found that under the right conditions, that dust could get trapped at the L5 point and remain there for a long time. The result of these simulations were dust clouds that mirrored the shape and size of what had been observed by the polarised imaging. Very small particles spread over a large area. So what is going on here? Why could some astronomers see these dust clouds and photograph them, while others claimed they didn't exist at all? The answer may lie in the structures themselves. Despite spanning roughly 100,000 km by 70,000 km, which is almost 9 times wider than the Earth, the total mass of the dust clouds is supposedly extremely small. Not to mention, the particles themselves are likely micron or submicron sized, a similar size to many bacterial cells, according to observations from the polarised imaging of L5. A micron is already a very tiny measurement, at one millionth of a metre. Individual particles of this size are only visible through a powerful microscope. Not only are the KDCs composed of these micron or submicron dust particles, sparsely spread across a wide area and nearly invisible to the naked eye, but the recent models made by Slis Barlow and Horvath in 2018 suggest that the shape of the L5 dust cloud also appears to be dynamic. The models point to the structure being non-uniform, with dust particle density varying across the KDC, and changing over time in synchrony with the Moon's orbital period. This could also support the idea that KDCs are not a stagnant accumulation of dust, but rather that they may be continuously losing and refreshing their contents, kind of like an ever-evolving dust storm, rather than a fixed, stable cloud. Things like solar wind or gravitational pull from the Sun or other planets may disrupt the delicate equilibrium that holds together these dust clouds, causing them to disperse before reforming again. This combination of extremely tiny particles that are dispersed over a large area, and the possibility that these clouds may form, disperse, and reform again and again over time could help to explain the discrepancy in observations over three decades. However, the tentative confirmation of the L5KDC in 2018 still leaves open scientific debate as to whether these clouds exist continuously, or whether they appear and disappear, depending on the influence of the Sun and other planets. Plenty of questions remain about Kordolevsky dust clouds, but one thing is certain, these These observations are not just a mirage, but a real phenomenon within our Earth-Moon system. Even though aspects of their structure, evolution, and composition remain under investigation, there is broad acceptance that KDCs are worthy of further study. While these so-called ghost moons that orbit the Earth-Moon Lagrange points may seem otherworldly, planet is no stranger to additional moons. In fact, Earth has had several mini-moons and quasi-moons before, albeit very different from the KDCs. For one thing, mini-moons typically come and go within a year, while the gravitational traps or Lagrange points, which are theorised to cause these Kordilevsky dust clouds, have existed since our Earth-moon system formed, making the KDC phenomenon potentially billions of years old. world. Another distinct difference is that mini-moons and quasi-moons are solid objects, whereas dust clouds are of course clouds of loose dust Quasimoons get their name because from one vantage point they look as if they are true moons orbiting the Earth However with a wider view these turn out to be asteroids orbiting the Sun. Mini-moons, on the other hand, are objects that really orbit a planet. They tend to be quite small and difficult to detect, which is probably why we've only ever managed to identify four mini-moons, none of which are orbiting Earth anymore. Take for example the mini-moon called 2020 CD3, which I discussed in a previous video. This small natural satellite was captured in Earth's orbit between January 2019 and May 2020, temporarily giving our planet a second moon. Well, mini-moon. In my opinion, our planet's possible ghost moons are perhaps the most exciting of these obscure types of moons, because of how unique they are. Despite being dynamic structures, these dust clouds are a long-term feature of our Earth-Moon system, and we still have so much to learn about them. Observing these dust clouds has tested the limits of our observational abilities, and as our technology and science improves, so can our understanding of KDCs. We should aim to build up more observation data of the L4 KDC, as this feature is historically underrepresented compared to the cloud at L5. We could also resurvey the clouds using methods like radar to see if technological improvements can yield different results compared to the negative detections of the past, as this would further establish the presence of these elusive features and fend off any lingering sceptics. But now that they've been broadly accepted by the scientific community, future research can begin to explore how KDCs are replenished over time, their potential impact on space weather, and their influence on satellite operations. Whether KDCs exist continuously, or appear and disappear over time, at least now we know that something really is out there, and we can study them with the right focus. These ghostly dust clouds continue to haunt our skies, reminding us that even the faintest, spooky traces of cosmic apparitions can hint at something palpable, and is worth investigating. 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 6km 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 universe. Our solar system isn't even heading right towards it. We are in it, charging for its point of origin head first. Welcome to our local hot bubble. What scientists now realise is the local environment that exists around our solar system. It is a neighbourhood 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? I'm Alex McColgan, and you're watching Astrum. Join me today as we walk in the aftermath of exploding stars and discuss how scientists even determined we were in the heart of a cataclysm to begin with. 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 hypothesised to be a large cavity in the interstellar medium, called a superbubble, 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 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. 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 IN60 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. And 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 crust 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, just 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 John Wallner, 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 suggests that there were a series of supernovae that occurred one after another in close succession. Astrophysicist Dieter Breitschwert, 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, whose surviving members are now associated with the Scorpius-Centora 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 supernovae exploded millions of years ago. The speed of expansion has plateaued at about 6 km per second now, according to astrophysicist Katherine Zucker. In 2022, Zucker authored a groundbreaking paper that reconstructed the evolution of our galactic neighbourhood, 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 the European Space Agency's Gaia telescope, Zaka and her team were able to construct a 3D space-time 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. Stellar nurseries are a field we're learning more about all the time, particularly as new images are taken by our telescopes. Here's a spectacular image of the Chameleon 1 dark cloud, one of our nearest stellar nurseries, taken by a dark energy camera on the Victor M. Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory. By studying the propagation of starlight from within it, scientists can tease out details about how stars form, which might help us better understand the local hot bubbles' impact on our galaxy today. You might not have seen this particular image before, as new space news is coming out all the time, but I've talked about it in my newsletter, I've recently launched to help you keep up with all the breathtaking photos released by our many telescopes on Earth and in orbit, or new breakthroughs that reshape how we understand the cosmos. You should sign up to never miss the most exciting news, even if the headlines do, by following the link in the description below. There are new editions that come out every Thursday. From the local hot bubble's birth 14 million years ago, Zucca 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 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 Ophiuchus stellar populations are born in the first epoch. 6 million years ago, the second star-forming epoch formed Corona Australis, and the older stars of Taurus. Then, around 2 million years ago, the stars in Lupus and Chameleon, as well as younger stellar populations of Taurus and Ophiuchus, came to be in the 3rd epoch. And finally, our present time falls within the 4th 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 sun'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 density Look this 3D map from Zucker 2022 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, sky, we don't have much to worry about. Tracking temperatures within the local bubble has provided more evidence of its existence. The Extended Röntgen Survey with an Imaging Telescope Array, better known as the E-Rosista 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 detail than before. Launched aboard the joint Russian and German mission Spectrum Röntgen Gamma in 2019, data from the E. Rosita 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 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 disk. 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 neighbourhood. 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 superbubbles seem likely to be common in our galaxy, creating a Milky Way 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 disk, and is believed to connect our local hot bubble to the Gum Nebula, or another larger nearby Superbubble. But the 3D map also revealed another, previously unknown interstellar tunnel, stretching towards the constellation Centaurus, possibly connecting our local bubble to the neighbouring Loop 1 Superbubble. While these interstellar tunnels are tantalising, our current understanding of them is limited. Nevertheless, these tunnels of hot gas and bubbles of star formation, shaped by the death of gigantic older stars, has me in awe of how powerful and interconnected the evolution of our local galactic neighbourhood 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. So next time you look up at the night sky, you might remind yourself that we are surrounded by crazy patterns, just like our local bubble in the Milky Way that was carved out by ancient cataclysms, and that some of those stars that you see are actually plastered along the walls of a supernova-blasted cavity, which connects to other parts of the galaxy through interstellar tunnels. Wow. In 2022, this astonishing image was published. What makes it so astonishing? Well, Well, this is one of the most detailed radio images of the centre of our galaxy that's ever been produced. Assembled from the first survey using the full array at the Meerkat Radio Observatory in South Africa, this image took three years of data analysis to complete, and it is revealing something thoroughly bizarre. Deep within the turbulent chaos at the centre of the Milky Way are hundreds of highly ordered one-dimensional filament-like structures dangling inexplicably above and below the galactic centre. These enigmatic filaments stretch for up to 150 light-years, yet are only one to three light-years across. The big question is, what are these strange supersized strands? Now, scientists are trying to unpick this meerkat image to work it out. I'm Alex McColgan and you're watching Astrum. Join me today as we uncover the mysteries around one of the Milky Way's weirdest phenomena. We'll explore the happy accident that led to their discovery and the extreme characteristics that are leaving scientists baffled. The centre of the Milky Way, 27,000 light-years from Earth, is a place of violence. This innermost region, the central molecular zone, spans 1,600 light-years and is, by all accounts, the most extreme part of our galaxy. Density, temperature, and turbulent velocity, a measure of chaotic fluid motion, are around 1-2 orders of magnitude higher here than anywhere else in the galaxy. The cosmic ray energy density, a proxy for energetic activity, is 2-3 orders of magnitude higher. This region is home to vast complexes of molecular gas, about 20 million 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 4 million times the mass of our Sun at the very center of it all. These conditions are hugely exciting for astronomers, but they make the galactic center notoriously hard to image. Visible light can't penetrate the dense clouds of dust and gas, so researchers turn to other parts of the electromagnetic spectrum to lift the veil and reveal the secrets at the heart of the galaxy. Radio waves have the longest wavelengths of the electromagnetic spectrum, from a few millimetres to hundreds of kilometres, and the wavelengths in the range of millimetres to tens of metres 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, Ferhad Yusuf 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 centre. 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 artefacts 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 artefacts, he returned to the VLA to image again at another frequency. And that was when his eureka moment struck. At 4am 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 artefact. This was a very real finding, something unlike anything he, or anyone else for that matter, had come across before. Zade 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 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, Zade 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 corroborated 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 begged 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 localised events like star formation or supernova remnants. So Zade dubbed them 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 Zade had many more questions. Where did the non-thermal filaments come from? 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 categorised. 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 Meerkat's mind-blowing image. The Meerkat radio telescope at the South Africa Radio Astronomy Observatory, or Tharao, is comprised of 64 interlinked antennas, each with a 13.5m diameter parabolic dish, spread over 8km 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 centre of the Milky Way, thanks to our Sun's axial tilt relative to its own position in the galaxy. So, Meerkat has a direct line of sight into the CMZ and the galactic centre. Over the course of three years, an international team led by Dr. Ian Hayward, and including Zadeh, now professor at Northwestern University, directed Meerkat 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 1712 MHz, 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, 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 visualising 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 meerkat 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 to enormous structures known as radio bubbles. First discovered by Hayward, Zadeh, and the Meerkat 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 outburst 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 and 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 a meerkat 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 Meerkat, 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 stretched magnetic field lines channeling them to produce the filament's signature synchrotron emission. With this hypothesis in mind, Zade 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 the mystery this tantalising, other astronomers have been studying the filaments too. But this single image is still the one that's told us the most. Zade 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 centers 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. Meerkat's detailed imagery of non-thermal filaments and the radio bubbles provides us with compelling evidence that this outflow of energy could happen in discrete but powerful outbursts. And this is something that has 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, coloured magenta in this image, are thought to be millions of years old, likely caused by a violent outburst from Sagittarius A star, which calculations suggest 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 mysteries 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 Meerkat, 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 kilometer 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. There's an elegance in order rising out of chaos, and observing non-thermal filaments streaming out through the cosmic winds certainly fits that notion. So keep watching this space, and with images and phenomena this spectacular, I certainly have no problem doing that. If you've been following the Astrum Answers series recently, you'll notice that we've talked a lot about how the universe is structured. Filament structures of galaxies being pulled apart by the universe's expansion, with bubbles or voids forming in the gaps. Because of the universe's expansion, everything is moving away from everything. But of course, this isn't totally true in practice due to a mysterious force called gravity. Gravity is a pulling force, or technically, it is the curvature of spacetime caused by uneven distribution of mass. On very small scales, gravity is hardly relevant at all. I don't feel any pull towards objects around me, only towards the Earth because it is so massive. Celestial objects close enough to the Sun are most influenced by its gravity, and all stars in the galaxy orbit around a supermassive black hole at the galaxy's core. But it doesn't stop there. You've probably heard that the Andromeda galaxy is hurtling towards us. How can that be when everything is moving apart? Gravity. Objects that are close enough together with a large enough mass are pulled towards each other by gravity faster than the universe can expand. This is why we have galaxy superclusters, and in fact we are part of one. Gravity is keeping these galaxy clusters bound together, meaning over extremely large timescales, collisions aren't totally unusual. In fact, a new theory has recently been proposed that the Milky Way may have recently experienced a collision with a large Magellanic Cloud-sized diffuse galaxy called Antlea 2. Scientists have discovered that the Milky Way has ripples consistent with it having had a collision in the past, but we couldn't pinpoint what it collided with, until Gaia discovered the Antlea 2 galaxy hidden behind our galactic disk. This makes it very hard to spot, as although it is massive, it is very spread out due to the collision, and being behind our galactic disk makes it hard to see due to the stars and dust in the way. But that brings us onto the main topic of this episode, the Great Attractor. In an opposite vein from the Supervoids video, where there are regions of space where there is an almost total absence of mass for hundreds of millions of light years in any direction, The greater tractor is the biggest concentration of mass for hundreds of millions of light-years. It is so massive that even though our galaxy is between 150 to 250 million light-years away, we and all galaxies around it are currently moving towards it. Estimates put its mass at roughly 1,000 trillion suns, which is enough for many thousands of galaxies. But what could possibly be there that is that massive? Well, for the longest time, it was a total mystery, because, like Antlia 2, the region where the greater tractor is located is hidden behind our galaxy's disk. However, X-ray telescopes can see through the disk, and recent technological improvements and advances in X-ray telescopes have meant that we have been able to detect thousands of galaxies in the region where the greater tractor is supposed to be. But the mass detected didn't add up. wasn't enough present to create such a pull. Further analysis has revealed something very interesting, that while we are being pulled towards the Great Attractor, there is something even more massive behind it, located 650 million light years away, called the Shapley Attractor or the Shapley Supercluster. Located there are many thousands of galaxies densely packed together with a mass of 10,000 trillion suns, and everything within 1 billion light years is being pulled towards it. On the other hand, looking the opposite direction from the Shapley supercluster, we see an underdense region, where everything seems to be moving away from it, called the dipole repeller. It isn't actually repelling mass, but due to all the mass around it being pulled towards more dense regions by gravity, it creates the illusion that it is repelling that mass, Although there are some scientists that do claim that an unknown repelling force is at work there. Simply put, we are still in very early days when it comes to understanding the universe. We do observe certain things, like the motion of galaxies, dense galaxy groups, and absences of galaxies in large voids or repelling regions. We observe the expansion of the universe, and observe the filamentary structures. But the universe is an impossibly large place, we can only see so far, only live so long. Plus, our technology is limited. We have theories which try and explain what we see, but I really wouldn't be surprised to see these theories change as more data becomes accessible. Some may ask, what's the point then? However, I for one am hugely grateful for the bright minds working on this, as discovering our place in the universe is so fascinating. I'm glad humans have an insatiable need to explore and understand everything around them. This innate sense of wonder and curiosity is what drives the evolution of mankind, and I am excited to witness it. A massive thank you to our astronauts on Patreon. This video had no sponsors, but it was still made possible thanks to the hundreds of members we have there. Link is in the description to join our growing community. Patreon is where Astrum truly takes shape. A place for people who love space, who want to see these videos keep improving and reaching more curious minds. Every new member keeps the channel focused on what really matters, making the complexity of space available to everyone. If you enjoy what we do, come join the Astrum community today.