UP-led astronomy research team explores formation of giant radio galaxies

Enabled by supercomputing, University of Pretoria (UP) researchers have led an international team of astronomers that has provided deeper insight into the entire life cycle (birth, growth and death) of giant radio galaxies, which resemble “cosmic fountains” – jets of superheated gas that are ejected into near-empty space from their spinning supermassive black holes.

The findings of this breakthrough study were published in the journal Astronomy & Astrophysics, and challenge known theoretical models by explaining how extragalactic cosmic fountains grows to cover such colossal distances, raising new questions about the mechanisms behind these vast cosmic structures.

The research team – which was led by astrophysicist Dr Gourab Giri, who holds a postdoctoral fellowship from the South African Radio Astronomy Observatory at UP –  consisted of Associate Professor Kshitij Thorat and Extraordinary Professor Roger Deane of UP’s Faculty of Natural and Agricultural Sciences; Prof Joydeep Bagchi of Christ University in India; Prof DJ Sailkia of the Inter-University Centre for Astronomy and Astrophysics, also in India; and Dr Jacinta Delhaize of the University of Cape Town (UCT).

This study tackles a key question in modern astrophysics: how these structures, which are larger than galaxies and are made up of black hole jets, interact over cosmological timescales with their very thin, gaseous surroundings. 

“We mimicked the flow of the jets of the fountains in the universe to observe how they propagate themselves over hundreds of millions of years – a process that is, of course, impossible to track directly in the real cosmos,” Dr Giri explains. “These sophisticated simulations enable a clearer understanding of the likely life cycle of radio galaxies by revealing the differences between their smaller, early stages and giant, mature stages. Understanding the evolution of radio galaxies is vital for deepening our knowledge of the formation and development of the universe.”

“While such studies are computationally expensive,” Prof Thorat adds, “the team embarked on this adventure informed by the exciting, cutting-edge observations carried out by new-generation radio telescopes, such as the  South African MeerKAT telescope, which has been instrumental in providing us with the details of the structure of these cosmic fountains.”

Astronomers study galaxies for more than just the stars they can see, Dr Giri says. “We also look at many, often interrelated, phenomena. One of the most amazing things to see is when a supermassive black hole at the centre of a galaxy, which is relatively tiny in size compared to the galaxies they grow in, ‘wakes up’ and starts eating up lots of nearby gas and dust. This isn’t a calm, slow or passive process. As the black hole pulls in material, the material gets superheated and is ejected from the galaxy at near-light speeds, creating powerful jets that look like cosmic fountains. These fountains emit radio signals as the accelerated high-speed plasma matter generates radio waves. These signals are detected by very powerful radio telescopes, built through the collaborative efforts of multiple countries working together.”

With the recent advent of powerful and sensitive radio telescopes – such as MeerKAT in South Africa, the Low Frequency Array (LOFAR) in Europe and the Giant Metrewave Radio Telescope (GMRT) in India – astronomers are now detecting these fountains even in their faintest stages, Dr Giri adds.

“These advanced telescopes can capture the weakest signals from dying or fading parts of the jet, leading to new discoveries of more such extended sources that were previously undetectable.”

The study also implies that these giant jets may be more common than previously thought.

Since the discovery of these high-speed fountains in the 1970s, astronomers have been curious about how far the ejected matter travels before eventually fading out. The answer was astounding as they began to discover that cosmic jets travel vast distances – some reaching nearly 16 million light-years (nearly six times the distance between the Milky Way and Andromeda).

“I took on the challenge of developing theoretical models for these sources, rigorously testing the models with the advanced capabilities of modern supercomputers,” Dr Giri says. “This computer-driven study aimed to simulate the behaviour of giant cosmic jets within a mock universe, constructed according to known physical laws governing the cosmos. Our primary focus was to answer two questions: Is the enormous size of these jets due to their exceptionally high speeds; or is it because they travel through regions of space that are nearly empty of surrounding matter, offering minimal resistance to the jets’ free propagation?”

The UP-led study presents evidence that a combination of these considerations is a key aspect in the formation of these giant jets.

With the help of the supercomputing power of the Inter-University Institute for Data Astronomy (a collaborative network consisting of UP, UCT and the University of Western Cape), the international research team was able to analyse the vast quantities of simulated data, effectively spanning millions of years.

“These computer-based models, which simulate jet evolution in a mock universe, do more than explain the origin of most giant radio galaxies,” Dr Giri says. “They’re also powerful enough to address puzzling exceptions that have confused astronomers in this field. For example, they help explain how some cosmic fountains bend sharply, forming the shape of an X in radio waves instead of following a straight path, and clarify the conditions under which giant fountains can still grow in dense cosmic environments.” These findings can be tested further by radio astronomers using advanced telescopes.

“Studies like this lead the way in formulating our understanding of these wonderful objects from a theoretical perspective,” Prof Thorat adds. “ This provides a complementary picture to deep-sky observations by telescopes like MeerKAT and the upcoming SKA, making simulations a key tool along with artificial intelligence techniques and high-performance computing to maximise the discovery space and optimise the scientific understanding of these and other ‘exotic’ objects.” 

Prof Sunil Maharaj, Vice-Principal for Research, Innovation and Postgraduate Education at UP, noted that the University is proud of the rapid growth of its radio astronomy research group.

“This was enabled by strategic investment in the Inter-University Institute for Data Astronomy and key personnel focused on science with world-leading African telescopes,” he says. “It’s just one example of UP’s leadership role in harnessing cutting-edge technology that increases Africa’s contributions to pushing scientific frontiers while developing the next generation of researchers on the continent. The research we are doing today is opening up new worlds and possibilities for the future.”

Disclaimer for banner image: An artistic representation of a what a giant cosmic jet the size of the distance between the Milky Way and Andromeda could look like (image for illustrative purposes only).

Researchers

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  Dr Gourab Giri

  Astrophysics researcher Dr Gourab Giri holds a Master of Science which he obtained from Presidency University in Kolkata in India as well as a doctorate from the Indian Institute of Technology in Indore.

  Through his research, he seeks to deepen our understanding of the fundamental processes that shape the universe, from galaxy evolution to cosmic origins. His research focuses on exploring various aspects of galaxy evolution in the cosmos, ranging from the role of supermassive black holes within galaxies to the evolution of galaxies within larger cosmic structures, such as galaxy clusters, where hundreds of galaxies come together. 

  Dr Giri’s current research goal is to develop a comprehensive model for extragalactic jet physics. This novel approach has the potential to unify and address multifaceted phenomena within a single framework, paving the way for deeper insights and broader applications in the field.

  “I am deeply engaged in leading research on various astrophysical topics,” he says. “Addressing the extensive datasets involved often necessitates the use of modern techniques, such as machine-learning. UP has access to one of South Africa’s premier supercomputing resources, which is essential for conducting high-resolution simulations and complex data analyses that are critical to my research. Additionally, the presence of a well-established radio astronomy group with expertise in observational techniques and the use of cutting-edge telescopes like MeerKAT makes UP an exceptional choice that aligns perfectly with my research objectives.”

  For Dr Giri, astrophysics inspires curiosity and critical thinking across generations, encouraging future scientists and innovators to address some of the most pressing global challenges.

  “Beyond its intrinsic scientific value, this field drives technological innovation, with advancements in high-performance computing and data analytics finding applications in rocket science, climate modelling and space weather prediction, which help protect vital satellite infrastructure,” he adds.

  His research matters, he says, because it satisfies our curiosity about how the universe functions, offering answers to fundamental questions about galaxy evolution.

  “This pursuit provides me with immense personal joy, which is essential to my well-being. The techniques and models I develop, such as advancements in big data handling and machine-learning, will not only enhance our understanding of the cosmos but also be transferable to other fields, such as space weather prediction, thus benefitting a broad range of scientific domains.”

  His message to undergraduate students is simple: “Stay curious, persevere and be patient; get involved in learning; and remember, hard work never fails.”

  When he is not trying to unravel the mysteries of the cosmos, Dr Giri enjoys writing sci-fi and adventure stories, and using his writing skills to convey his research to others.

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  Professor Kshitij Thorat

  Professor Kshitij Thorat is an astronomer and an associate professor at the University of Pretoria (UP). He is a member of UP’s astronomy group within the Department of Physics at the Faculty of Natural and Agricultural Sciences. He specialises in doing research with the MeerKAT telescope and using artificial intelligence (AI) in astronomy. He’s part of the team that has solved the mystery of X-shaped radio galaxies with the help of striking images from the MeerKAT telescope and second author of the study whose results will be published in the Monthly Notices of the Royal Astronomical Society (with a pre-print available here).
  
  What is your academic background?
  
  I have been doing radio astronomy ever since my days as a PhD candidate, when I helped survey a large area of the sky as seen in “radio” light. Following that, I have been working as a postdoctoral fellow in South Africa for nearly five years. The focus of my research has been objects powered by supermassive black holes jets in the distant universe. One of the main reasons I chose to come over to South Africa for postdoctoral work was the appeal of the MeerKAT telescope, which back then was under construction, and which excels in making detailed images of such objects. My time at Rhodes University as a postdoctoral fellow gave me a chance to participate in some of the very first studies done with MeerKAT. So far, I have co-authored eight publications based on MeerKAT observations and several more are on the way. Many of these have been published in the last year or two, after the inauguration of the telescope. Last year, when a call was made for observation proposals using MeerKAT, we submitted a proposal (one of the only 38 proposals which were accepted) to study a carefully selected sample of X-shaped sources, expecting the telescope to produce images of unprecedented quality. This expectation has been borne out fully. Of course, since MeerKAT (and other telescopes) produce such a large amount of data compared to older telescopes, we need to use a lot of automation and smart algorithms to analyse the data efficiently and effectively. I am an expert in the data-intensive process of converting the petabytes of raw data to beautiful images such as the one seen in this press release. I also focus on machine learning techniques to solve issues arising from the transition of astronomy towards big data regime. One of the issues I am especially interested in is automatically identifying sources with unusual morphologies, for example, X-shaped galaxies. Along with Dr Arun Aniyan, my colleague, I have made a tool to identify radio sources using what are known as convolutional neural networks. We were the first to use this technique in radio astronomy. Since then, the field has advanced quite a bit. We have an active collaboration with UP’s Computational Intelligence Research Group (CIRG), with co-supervised students pursuing AI-enhanced astronomy projects, and this is an ideal place to further this line of research.
  
  How did you become interested in astronomy?
  
  That was a long time ago, when I was still an undergraduate student. Astronomy back home in India was really taking off and one had access to a lot of material on astronomy at a popular level. It was really the amazing pictures of our universe which made me interested in astronomy.
  
  Tell us a bit about how this discovery sheds light on previous ideas and how it changes everything we know about X-shaped galaxies?
  
  Currently there are several ideas on how X-shaped galaxies come by their shape. Two of the most interesting ones are that either something changes in the engine which powers these sources - a supermassive black hole sitting at the centre of the galaxy, or that it has to do with the environment in which these sources sit. You could compare it to the nature-vs-nurture debate in the field of psychology. In this particular case, we found several pieces of definite evidence that the X-shape is caused by the latter explanation. This was suspected through earlier studies of this source, but the far superior observations with MeerKAT were instrumental in confirming the correct formation scenario. The jury is still out on whether most (if not all) X-shaped galaxies are formed in such a way, but we are working on that with further MeerKAT observations of more galaxies.
  
  Radio astronomy has taken off in recent years with South Africa playing a leading role because of MeerKAT and the Square Kilometre Array, how much more is there still to do to make it a mainstream field of study in SA?
  
  We are still a small community in South Africa but with a huge interest from students who want to pursue astronomy at a postgraduate level. The research group at UP has grown quickly, becoming a significant component with the Department of Physics in a short space of time. I would say the next five years will determine to what degree astronomy becomes ‘mainstream’ at UP and in South Africa in general.
   

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  Professor Roger Deane

  University of Pretoria (UP) astrophysicist Professor Roger Deane was part of the international group of scientists who have captured the first image of a black hole. His group worked to develop simulations of the complex, Earth-sized telescope used to make this historic discovery. These simulations attempt to mimic and better understand the data coming from the real instrument, which is made up of antennas across the globe.
  
  About four years ago, Prof Deane started working with the team on the Event Horizon Telescope (EHT), which captured the image that was globally released today (Please see up.ac.za for the official media release). Prof Deane, who grew up in Welkom in the Free State, developed a passion for astronomy from an early age, when he was dazzled by the excellent view of the Milky Way.
  
  Downplaying his contribution to the capturing of the first image of a black hole, the 36-year-old Associate Professor of Physics said, “I’m still blown away by the image. It hasn’t really worn off yet. I’m just proud and honoured to play my small part in this amazing international team.”
  UP Vice-Chancellor and Principal Prof Tawana Kupe congratulated Prof Deane on his contribution to the EHT. "This young scientist is an inspiration to scientists on the African continent. Our staff and students are innovative and creative thinkers who excel in cutting-edge research, and this discovery is a great example of what can be achieved if we work together across borders and disciplines. UP is already at the forefront of world-class research and, as one of the largest knowledge producers in South Africa, we make an impact on issues of critical relevance to Africa and the world. We produce high-quality research that matters,” he said.
  
  According to Prof Deane, as with any major physics experiment, one needs to understand the effects that the instrument itself may have on the data. “In the case of the EHT, we built a simulation package that physically modelled a number of non-desirable effects that prevent one from seeing any sort of black hole shadow feature.”
  
  The EHT observes what radio astronomers consider to be a very short wavelength, about 1 mm, which means the distance between two consecutive peaks of light is 1 mm. “This is about 200 times smaller than the wavelength of light that MeerKAT observes, and presents many challenges to the telescope design, data processing and analysis.”
  
  Prof Deane said, “Just a small amount of water vapour in the atmosphere could completely erase the signature of the black hole shadow. This is why the EHT stations are at very high altitudes in some of the driest places on Earth.” There are a multitude of other aspects to accurately model in an instrument as sensitive and complex as this telescope. “We incorporate as much of this information as we can physically model in software. This accurate simulation of the telescope enables astronomers to better understand the real observations, discriminate between theoretical black hole shadow models, and insights into the characteristics and performance of the telescope itself.” He explained that this also allows scientists to accurately predict the impact of adding new antennas in the global network, as is planned for the African Millimetre Telescope (AMT) project in Namibia.
  
  The first image of a black hole is a significant milestone for the EHT, but much lies ahead as the team works towards testing Einstein’s general theory of relativity. To do so, they will need to continue to improve the images through array expansion in Africa and elsewhere with improved algorithms. Prof Deane says his group is now focused on three things: “Expanding our simulations to model the case where light from the black hole may have preferred orientation – think about how polarised lenses reduce the sun’s glare from the sea – performing detailed simulations on new prospective sites, and exploring a range of probabilistic modelling techniques to extract the properties of the black hole shadow.”
  
  What did it feel like being part of a team of 200 highly talented scientists who have worked on this project?
  
  “It has been a privilege – I have learned a great deal in all spheres. One of the aspects of my job that I love the most is working with astronomers from around the world from a diverse set of backgrounds and perspectives. The dramatic result unveiled today has required a combination of the world’s best engineers, theorists, and observers. I’m thrilled to be a part of that team. It has also been challenging, apart from practical aspects like the geographic and time zone differences.”
  
  At UP, this Y1 National Research Foundation-rated scientist is leading the new Astronomy Research Group which is focused on MeerKAT, the Square Kilometre Array, and the technique of creating virtual Earth-sized telescopes like the EHT and the African Very Long Baseline Interferometry Network.
  
  When he moved to UP in January 2018, there were no other astronomers at the institution. “By July, we should have scaled up to approximately 14. We are hoping to finalise a joint South African Radio Astronomy Observatory-UP South African Research Chair Initiative Chair in radio astronomy by then as well. Over 100 UP students registered for the first year astronomy course in 2019, a dramatic increase, so there is clearly a need to grow the number of faculty positions in astronomy to deal with the teaching and postgraduate student supervision demand.”
  
  The UP Astronomy group’s science-driven approach is in keeping with the realisation that this new era of complex, big-data telescopes requires technical expertise and new algorithmic approaches. A significant part of his UP research group’s work is focused on machine learning with the UP Computational Intelligence Research Group in the Department of Computer Science, and instrumental work in collaboration with UP’s Electrical, Electronic and Computer Engineering Department.
  
  Looking ahead, Prof Deane is very excited about growth in astronomy, saying that, “South Africa has an increasing number of astronomy-related success stories to help spur our youth into science and technology careers. I think our government, through the Department of Science and Technology, has been very strategic in that regard, with payoffs that will be far-reaching and long-lasting.”
  
  Professor Roger Deane on the University of Pretoria’s astronomy programme
  
  When did UP’s astronomy programme start?
  
  UP’s Department of Physics has had astronomy undergraduate courses for many years. The current radio astronomy research group started at the beginning of 2018 with my arrival. UP has among the largest astronomy enrollments in undergraduate courses in South Africa, showing great potential to grow into a large research group.
  
  Approximately how many students do you have?
  
  In July this year, we should have scaled up to approximately 13 (1 faculty, 2 post-docs, 1 PhD, 3 MSc, 6 Hons). We are hoping to finalise a joint South African Radio Astronomy Observatory-UP SARChI Chair in radio astronomy by then as well, which should increase the cohort to at least 20.
  
  Why is big data important, and what is the computational capacity of the MeerKAT and the Event Horizon Telescope (EHT)?
  
  The EHT raw data was 4 petabytes in size. Unlike EHT, which observes one astrophysical object a time, MeerKAT will detect many millions and have archive sizes even larger than an annual EHT campaign. To analyse this data and ensure we enable all the exciting discoveries to come, we have to get in step with the fourth industrial revolution (4IR) and employ artificial intelligence and machine learning approaches. Astronomy is a key contributor to the 4IR, as highlighted by President Cyril Ramaphosa in this year's State of the Nation address. At UP, the Astronomy and Computational Intelligence Research Groups are working closely together to ensure our university plays a leading role in this en route to the Square Kilometre Array. The UP Astronomy group’s science-driven approach is coupled with the realisation that this new era of complex, big-data telescopes requires technical expertise and new algorithmic approaches. A significant part of the UP research group’s work is focused on machine learning with the UP Computational Intelligence Research Group in the Department of Computer Science, and instrumental work in collaboration with UP’s Electrical, Electronic and Computer Engineering Department.
  
  How is UP leading in investing and promoting astronomy as an academic and research discipline?
  
  UP has taken a forward-thinking, strategic approach by investing in the Inter-University Institute for Data Intensive Astronomy (IDIA). It is one of three university partners who are ensuring they will be able to deal with the data processing and analysis demands of MeerKAT and SKA. UP has also taken a strategic decision to invest in the technique of Very Long Baseline Interferometry – the very same approach the EHT uses. This is with a view to taking a leadership role in the African VLBI Network and the second phase of the Square Kilometre Array, ensuring South Africa and Africa are at the forefront of the spectacular science these VLBI arrays will perform.
  
  How does UP’s astronomy programme – and South African astronomy in general – measure up in the global astronomy community?
  
  In the UP Department of Physics, we are building a new astronomy group that is both science-driven and technically savvy. We have demonstrated that in the EHT project, and we are heavily focused on making leading contributions towards MeerKAT, which will eventually extend across the African continent as the SKA. It's important that South Africa benefit scientifically from the astronomy investments that the South African government has made through the Department of Science and Technology. To do so, universities need to play their part in investing in research expertise. UP is in the process of stepping up to that responsibility, with this EHT announcement being a first example of the fruits of that investment.

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Related Infographic

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  How big are Giant Radio Galaxies?

Related Photo

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  How far do these cosmic jets travel?