We have found several strange radio sources in a distant cluster of galaxies. They force us to rethink what we thought we knew.

Electromagnetic view of the colliding cluster Abell 3266 using data from ASKAP and ATCA (red/orange/yellow), XMM-Newton (blue), and dark energy research (background map). (Image credit: Christopher Risley (University of Bologna)).

This article was originally published in The Conversation. (will open in a new tab) The publication published an article in Expert Voices: Op-Ed & Insights on

Christopher Risley (will open in a new tab)researcher at the University of Bologna
Tessa Wernström (will open in a new tab)senior fellow at the University of Western Australia

The universe is dotted with clusters of galaxies, huge structures piled up at the intersections of the cosmic web. (will open in a new tab). A single cluster can span millions of light-years across and contain hundreds or even thousands of galaxies.

However, these galaxies make up only a few percent of the total mass of the cluster. About 80% of it is dark matter, and the rest is hot plasma “soup”: gas heated to temperatures above 10,000,000 degrees Celsius and entwined with weak magnetic fields.

We and our international team of colleagues have identified a number of rarely observed radio objects — a radio relic, a radio halo, and radio fossils — in a particularly dynamic galaxy cluster called Abell 3266. They challenge existing theories about the origin of such objects. and their characteristics.

Relics, halos and fossils

Galaxy clusters allow us to study a wide variety of processes, including magnetism and plasma physics, in environments that we cannot recreate in our laboratories.

When the clusters collide with each other, a huge amount of energy is injected into the hot plasma particles, generating radio emission. And this problem comes in all shapes and sizes.

Radio Relics is one example. They are arc-shaped and located at the fringes of the cluster, driven by shock waves passing through the plasma, which cause a jump in density or pressure and excite the particles. An example of a shock wave on Earth is the sonic boom that occurs when an aircraft breaks the sound barrier.

“Radiohalos” are irregular sources located closer to the center of the cluster. They are powered by turbulence in the hot plasma, which gives energy to the particles. We know that both halos and relics are formed as a result of collisions between clusters of galaxies, but many of their fine details remain elusive.

Then there are the “fossil” radio sources. These are radio remnants after the death of a supermassive black hole at the center of a radio galaxy.

When they operate, black holes release huge jets of plasma. (will open in a new tab) far beyond the galaxy itself. When they run out of fuel and shut down, the jets begin to dissipate. The remains are what we find as radiofossils.

Abel 3266

Our new newspaper (will open in a new tab)published in the Monthly Notices of the Royal Astronomical Society, presents a very detailed study of a cluster of galaxies called Abell 3266.

It is a particularly dynamic and erratic colliding system located about 800 million light-years away. It has all the hallmarks of a system that should have relics and halos, but nothing has been discovered until recently.

Continuation of work carried out using the Murchison Widefield Array (will open in a new tab) Earlier this year (will open in a new tab)we used new data from the ASKAP radio telescope (will open in a new tab) and the Australian Telescope Compact Array (will open in a new tab) (ATCA) to see Abell 3266 in more detail.

Our data paints a complex picture. You can see this in the main image: the yellow color shows the functions where energy input is active. The blue haze is hot plasma captured in X-rays.

Redder colors show features that are only visible at lower frequencies. This means that these objects are older and have less energy. Either they have lost a lot of energy over time, or they never had much to begin with.

The radio relic is highlighted in red at the bottom of the image (see enlargement below). And our data here reveals special features that have never been seen before in a relic.

The “wrong path” relic in Abell 3266 is shown here in yellow/orange/red, representing radio brightness. (Image credit: Christopher Risley using data from ASKAP, ATCA, XMM-Newton and dark energy research))

Its concave shape is also unusual, earning it the catchy nickname of the “wrong way” relic. Overall, our data is disrupting our understanding of how relics are generated, and we are still working on deciphering the complex physics of these radio objects.

Ancient remnants of a supermassive black hole

The radio fossil, visible in the upper right corner of the main image (and also at the bottom), is very faint and red, indicating that it is ancient. We believe that this radio emission originally came from the galaxy in the lower left corner with a black hole in the center, which has long since been switched off.

The radio fossil in Abell 3266 is shown here in red colors and outlines representing the radio brightness measured by ASKAP and blue colors showing hot plasma. The blue arrow points to a galaxy we think once harbored the fossil. (Image credit: Christopher Risley, using data from ASKAP, XMM-Newton and dark energy research)

Our best physical models simply can’t fit the data. This reveals gaps in our understanding of the evolution of these sources – gaps that we are working to fill.

Finally, using a clever algorithm, we defocused the first image to find a very faint emission invisible at high resolution, revealing the first detection of a radio halo in Abell 3266 (see below).

The radio halo in Abell 3266 is shown here with red colors and outlines representing the radio brightness measured by ASKAP and blue colors showing hot plasma. The dotted blue curve marks the outer boundaries of the radiohalo. (Image credit: Christopher Risley, using data from ASKAP, XMM-Newton and dark energy research)

Towards the future

This is the beginning of the journey to understanding Abell 3266. We found a lot of new and detailed information, but our research raised even more questions.

The telescopes we have used are laying the foundation for revolutionary science from an array of square kilometers. (will open in a new tab) project. Research like ours allows astronomers to figure out things we don’t know, but you can be sure we will.

We recognize the Homeroi people as the traditional owners of the ATCA site, and the Wajarri Yamatji people as the traditional owners of the Murchison Radio Astronomy Observatory site, where ASKAP and the Murchison Widefield Array are located.

This article is republished from The Conversation (will open in a new tab) under a Creative Commons license. Read original article (will open in a new tab).

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