Astronomers are discovering things that were once hidden inside some of the largest objects in the universe, known as galaxies. Using the powerful MeerKAT radio telescope in South Africa, researchers have mapped the extinction, the scattering of radio emissions, a signal that reveals the energetic processes that occur in the large spaces between galaxies when galaxies collide or merge.
Konstantinos Kolokythas, a radio astronomer and postdoctoral researcher at Rhodes University and the South African Radio Astronomy Observatory (SARAO), has led research into what these emissions reveal about our cosmic history. His findings shed light on what powerful instruments like MeerKAT and the upcoming Square Kilometer Array (SKA) will discover as they probe the invisible radio universe.
What did MeerKAT find, thanks to its understanding?
Think of a galaxy not as a collection of thousands of stars, but as a bustling city. While telescopes usually see the “bright lights” of individual galaxies, MeerKAT helped us detect the faint “smoke” or “fog” that fills the streets between them. Our search was for “radio advertising” very narrowly. It is spread over millions of light years, like a thin, shimmering mist.
In the vast spaces between galaxies lies the Intracluster Medium – the incredibly hot, thin gas that fills the cluster. Although the gas itself is often seen with X-ray telescopes, it also contains magnetic fields and electrons that travel at nearly the speed of light.
When galaxies collide, it’s like a cosmic dance: electrons that collide with the magnetic field are forced around the magnetic field lines, emitting energy like radio waves. This is the radio emission we see at 1.28 GHz with MeerKAT. It reveals areas of accelerative shocks (the effects of cosmic collisions).
Our research within the MeerKAT Galaxy Cluster Legacy Survey (MGCLS), a program led by the South African Radio Astronomy Observatory, used this capability to map 115 of these “cosmic cities”. We identified 103 published sources, including 60 structures that were not visible at all in previous generations of telescopes. The legacy survey also produced its own summary.
In fact, we have gone from having a blurry map of the environment to a high-definition atlas, which reveals that the “empty” space between the galaxies is actually full of energy. By combining these radio and X-ray data with the optical ones, we can calculate the “energy balance” – essentially a complete record of all the energy, heat and gravity moving through these gigantic structures.
How does this clarify or add to what was previously known?
Before this work, we only saw the brightest, most violent events of the convention. With our new catalog, we are able to see a broad picture of the evolution of the universe, to detect the smallest objects resulting from the collision of galaxies. By identifying these elements in more than half (54%) of the researched groups, we can learn how energy works on a universal scale.
These radio signatures are the “scars” left by mergers – large, slow-moving collisions where the gravitational pull of two massive galaxies pulls them together. This process creates turbulence and “kick” waves at extreme speeds.
Our research shows that these high-energy events are an important part of the life cycle of the group and the evolution of the universe. Bands that appear “quiet” or “quiet” on an X-ray often hide a history of radioactivity. We have been mapping the mysteries of gravity for billions of years. In radio astronomy, the universe is never truly silent.
What direction does this point for future research?
This list serves as a high-level “baseline” for the next ten years. With MeerKAT, we have pushed the limits even further, allowing us to see many sources in the “ultra-steep spectrum” – faint emissions from the oldest “tired” particles in the universe. These are important for understanding the long-term energy cycle of the universe.
Looking ahead, this research paves the way for the evaluation of the Square Kilometer Array (SKA), the world’s most sensitive radio telescope, which is expected to be fully operational by 2030. If MeerKAT can detect 60 new structures in a small area of the sky, the SKA will probably find thousands.
Why is this important?
Because these things made in groups are the biggest “laboratories of nature” in the universe. By studying them, we are not just looking at beautiful pictures; we are learning how gravity, magnetism and matter behave on a scale that is impossible to recreate and the human mind cannot imagine.
Read more: Astronomers used machine learning to mine data from South Africa’s MeerKAT telescope: what they found
This research proves that South Africa is at the forefront of this discovery, using local technology to answer deep questions about the fabric of our universe, where our universe came from and how it is changing.
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