Enabled by supercomputing, researchers from the University of Pretoria (UP) have made a remarkable breakthrough in understanding the life cycle of giant radio galaxies. These galaxies, often referred to as “cosmic fountains,” eject jets of superheated gas into near-empty space, powered by the supermassive black holes at their centers. The international team of astronomers, led by UP astrophysicist Dr. Gourab Giri, has provided deeper insights into the birth, growth, and death of these enormous cosmic structures. The study’s findings, published in the prestigious journal Astronomy & Astrophysics, not only challenge existing theoretical models but also open up new avenues for exploring the mechanisms behind the vast distances these cosmic jets can travel.
The Research Team and Methodology
Dr. Gourab Giri, a postdoctoral fellow from the South African Radio Astronomy Observatory at UP, led the research, supported by a team of prominent astronomers. The team included Associate Professor Kshitij Thorat, Extraordinary Professor Roger Deane, and other esteemed experts from institutions such as Christ University, Inter-University Center for Astronomy and Astrophysics (IUCAA), and the University of Cape Town (UCT).
The research sought to answer fundamental questions in modern astrophysics by investigating the interactions between these cosmic fountains and their gaseous surroundings over cosmological timescales. The astronomers used sophisticated supercomputing simulations to model the evolution of giant radio galaxies over millions of years, providing a clearer understanding of their life cycle.
Cosmic Fountains and Supermassive Black Holes
A giant radio galaxy forms when a supermassive black hole at the center of a galaxy “wakes up” and begins to consume surrounding gas and dust. This process is far from passive; the material gets superheated as it is pulled into the black hole and is then ejected as high-speed jets. These jets of plasma, or cosmic fountains, travel across vast distances, emitting radio waves as they propagate.
Dr. Giri explains, “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.” Using supercomputing simulations, the team sought to reveal the differences between the early stages of these radio galaxies and their mature forms, which can grow to enormous sizes.
The Role of Advanced Telescopes in the Study
The study was made possible by the cutting-edge observations provided by new-generation radio telescopes, such as the South African MeerKAT telescope, Low Frequency Array (LOFAR) in Europe, and the Giant Metrewave Radio Telescope (GMRT) in India. These telescopes have revolutionized the ability of astronomers to observe even the faintest signals from dying or fading jets. According to Dr. Giri, “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.”
One of the critical breakthroughs of this study is the finding that these cosmic jets can travel vast distances, some reaching as far as 16 million light-years—nearly six times the distance between the Milky Way and the Andromeda Galaxy. This discovery challenges earlier theories that suggested such jets would lose energy and fade much sooner.
Simulating the Evolution of Giant Jets
The research team used powerful supercomputers to simulate the behavior of giant cosmic jets in a mock universe. Their goal was to answer two pivotal questions:
- Is the size of these jets due to their high speeds?
- Do they travel through regions of space that are nearly empty, offering little resistance and allowing the jets to propagate freely?
Through supercomputing simulations at the Inter-University Institute for Data Astronomy, a collaborative network of UP, UCT, and the University of Western Cape, the team was able to analyze vast quantities of data, spanning millions of years. Dr. Giri notes, “These computer-driven studies do more than explain the origin of most giant radio galaxies. They also help to resolve some of the puzzling exceptions in this field, such as how cosmic fountains bend sharply or form X-shaped structures in the radio waves.”
The results of the study revealed that a combination of both high speed and the low-resistance environment through which the jets travel plays a crucial role in the formation and size of these cosmic fountains.
Implications for Understanding Radio Galaxies
The findings of the UP-led study have significant implications for the evolution of radio galaxies and the universe itself. While most models have focused on the internal mechanics of the jets and their speed, the UP team’s research shows that the cosmic environment plays a key role in how far and how long these jets can propagate.
Dr. Giri emphasizes, “Understanding the evolution of radio galaxies is vital for deepening our knowledge of the formation and development of the universe. These jets are much more than just a curiosity; they are a window into the larger processes governing the universe’s structure and development.”
The Mystery of X-Shaped Radio Sources
One of the key findings of the study was the ability to explain the formation of X-shaped radio galaxies—a phenomenon where the jets of plasma from the supermassive black hole appear to bend sharply, creating an X-like shape. These previously unexplained structures have been a source of intrigue for astronomers, but the simulations from this study shed new light on their origin.
The models showed that environmental factors such as the presence of dense surrounding gas, magnetic fields, and interactions with nearby galaxies can lead to the formation of these unique shapes. By using the simulations to model different cosmic environments, the researchers were able to explain how these jets can bend sharply and form these X-shaped structures.
The Future of Giant Radio Galaxies Research
The study raises new questions about the mechanisms that govern cosmic jets, particularly as they interact with the gaseous environments in which they propagate. By revealing the processes that govern the life cycle of these fountains, the research team has laid the groundwork for future studies that will focus on dense cosmic environments and high-speed jets in greater detail.
Astronomers are also looking forward to using these models to test the conditions under which giant fountains can continue to grow in more dense regions of space, offering further opportunities for discovery. The work is already influencing future observational strategies for advanced telescopes such as the Square Kilometre Array (SKA), which is set to revolutionize our ability to study cosmic jets and radio galaxies.
The Role of UP in Pushing Scientific Boundaries
Prof. Sunil Maharaj, Vice-Principal for Research, Innovation, and Postgraduate Education at UP, commended the university for its leadership role in radio astronomy and its commitment to using cutting-edge technology to explore the frontiers of science. He highlighted the growth of UP’s radio astronomy research group, which is powered by investments in institutions like the Inter-University Institute for Data Astronomy.
Prof. Maharaj said, “The research we are doing today is opening up new worlds and possibilities for the future. This is just one example of how Africa is contributing to global scientific advancement, leveraging world-leading technology and developing the next generation of researchers.”
Conclusion
This study represents a significant leap forward in our understanding of the life cycle of giant radio galaxies and the mechanisms behind cosmic fountains. By combining supercomputing power, advanced telescopes, and collaborative research from institutions across the globe, the team has provided new insights into the evolution of these giant cosmic structures. Their findings challenge existing models and raise fresh questions about the interaction between these jets and their environments, paving the way for future research in the field of astrophysics.
Reference: Gourab Giri et al, Probing the formation of megaparsec-scale giant radio galaxies, Astronomy & Astrophysics (2024). DOI: 10.1051/0004-6361/202451812