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In 2022, this astonishing image was published. [music] What makes it so astonishing? Well, this is one of the most detailed radio images of the center of our galaxy that's ever been produced. Assembled from the first survey using the full array at the MCAT 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 center of the Milky Way are hundreds of highly ordered one-dimensional filamentlike structures [music] dangling inexplicably above and below the galactic center. These enigmatic filaments stretch for up to 150 lightyear yet are only 1 to three lightyears across.
The big question [music] is what are these strange superersized strands? Now scientists are trying to unpick [music] this mircat image to work it out. I'm Alex Mccoan and you're watching Astramm. 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 center of the Milky Way, 27,000 light-years from Earth, is a place of violence. >> [music] >> This innermost region, the central molecular zone, spans 1,600 light-year and is by all accounts [music] the most extreme part of our galaxy. Density, temperature, and turbulent velocity, a measure of chaotic [music] fluid motion, are around 1 to two orders of magnitude higher here than anywhere else in the galaxy.
The cosmic ray energy density, a proxy for energetic activity, is 2 to three orders of magnitude higher. This region is home to vast [music] 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 supernova. And let's not forget Sagittarius a star, the super massive 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 [music] to image.
Visible light can't penetrate the dense clouds of dust and gas. So researchers turned 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 millime to hundreds of kilome and the wavelengths in the range of millime to tens of meters are ideal for radio astronomy.
They pass through the obscuring clouds of gas and dust, [music] giving us a clear view of what lies beneath. In the early 1980s, Furhad Ysef Zade, 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 400 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. 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 three 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 [music] by a standard distance of around one astronomical unit, the distance between Earth and the Sun.
When he cross-cheed them with the infrared data from that area, Zarde also discovered they had no counterpart in that area of the spectrum. This told him they were non-therrmal emissions. That is to say they were [music] not produced by heated gases. This was corroborated by other measurements such as spectral index and polarization which showed [music] that the filaments were highly magnetic and emitting synretron radiation.
Synrettron 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 werecontinuous ruling out localized events like star formation or supernova remnants.
So Zade dubbed them non-therrmal filaments and suggested they were likely related to galactic scale phenomena. For a scientist, a discovery like this would have been like Christmas coming early. After all, what do you get a budding scientist and a space enthusiast? Galactic structures of unknown origin that no one had ever seen before.
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His observations didn't correspond to anything else in the known galaxy, and Zarde 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-therrmal 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 Miacat's mindblowing image. The MICAT radio telescope at the South Africa radio astronomy observatory or saro is comprised of 64 interlin [music] antennas each with a 13.5 m diameter parabolic dish spread over 8 km [music] 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 [music] sun's axle tilt relative to its own position in the galaxy. So, Miaat has a direct [music] line of sight into the CMZ and the galactic center. Over the course of 3 years, [music] an international team led by Dr.
Ian Haywood and including Zarde, now professor at Northwestern University, directed Mia 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 Lband radio frequencies of 856 to 1,712 [music] MHz, equivalent to wavelengths of 18 to 35 cm.
They split this area into a 20part mosaic, directing the telescope to survey each tile in turn over a total of 144 hours on target. This was the first time Mircat'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 highpass 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-therrmal filaments.
And this is the result. More like a work of art than a scientific study, it captures a wealth of features. Some are wellnown 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 runaway pulsar, the mouse and up on the right one of the longest and most famous non-therrmal 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 gamechanging for Zard 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 setto 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 synretron radiation is a defining characteristic. Interestingly, the MICAT 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 too.
Enormous structures known as radio bubbles. First discovered by Haywood Zade and the Miacat team in 2019, these huge radio emmitting structures stretched 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-therrmal 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 mircat 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 Mircat, alongside the same highpass filtering used to resolve the non-therrmal 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 synretron emission. With this hypothesis in mind, Zard and the team described the formation of non-therrmofilaments as magnetized streamers in a cosmic raydriven 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.
Zard 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-therrmal radios 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 [music] there.
How super massive 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 [music] 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 [music] us.
But how this feedback happens is unknown. Mircat's detailed imagery of non-therrmal 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. Fermy bubbles discovered by NASA's Fermy gammaray telescope in 2010 are even bigger hourglass shaped configurations spanning a total of 50,000 lightyear.
These mindbogglingly 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 supernova. 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 scientistscontinue to unravel the mysteries of non-therrmof filaments and tackle the big questions about [music] how the universe works, the trail doesn't seem to be going cold again anytime soon.
Since the first full array image, Mircat 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 [music] 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 Mircat already awarded by the Royal Astronomical Society for its spectacular observations in radioastronomy was built with longerterm goals in mind namely to be incorporated into [music] the square kilometer array. With a total collecting area of one square km, it will be 50 times more sensitive than any other radio instrument in existence.
[music] 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. Zard 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 fermy bubbles are connected.
There's an elegance in order rising out of chaos and observing non-therrmal filaments streaming out through the cosmic winds certainly fits that notion. So, keep watching this space. [music] And with images and phenomena this spectacular, I certainly have no problem doing that. I'm happy to announce we have a weekly newsletter to keep up with all the discoveries in our cosmos.
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