The Universe is full of clusters of galaxies: huge structures stacked at the intersections of the cosmic web. A single cluster can span millions of light-years and be made up of hundreds, or even thousands, of galaxies.
However, these galaxies represent only a small percentage of the total mass of a cluster. About 80 percent is dark matterand the rest is a “soup” of hot plasma: gas heated to more than 10,000,000 ℃ and interwoven 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 a fossil radio emission – within a particularly dynamic galaxy cluster called Abell 3266. They defy theories. existing information about the origins of such Objects and their characteristics.
(Christopher Riseley, using data from ASKAP, ATCA, XMM-Newton, and the Dark Energy Survey)
Above: The colliding cluster Abell 3266 seen through the electromagnetic spectrum, using data from ASKAP and ATCA (red/orange/yellow colors), XMM-Newton (blue), and the Dark energy Survey (background map).
Relics, Halos, and Fossils
Galaxy clusters allow us to study a wide range of rich processes, including magnetism and plasma physics, in environments that we cannot recreate in our laboratories.
When the clusters collide with each other, huge amounts of energy are deposited into the hot plasma particles, generating radio emissions. And this issue comes in a variety of shapes and sizes.
“Radio relics” are an example. They are arc-shaped and settle towards the outskirts of a cluster, propelled by shock waves traveling through the plasma, causing a jump in density or pressure and energizing the particles. An example of a shock wave on Earth is the sonic boom that occurs when an airplane breaks the sound barrier.
“Radio halos” are irregular sources that are found towards the center of the cluster. They are powered by turbulence in the hot plasma, which energizes the particles. We know that both halos and relics are generated by collisions between galaxy clusters, but many of their gritty details remain elusive.
Then there are the “fossil” radio sources. These are the radio remains of the death of a supermassive black hole at the center of a radio galaxy.
when they are in action black holes shoot huge squirts plasma far beyond the galaxy itself. As they run out of fuel and shut down, the jets begin to dissipate. The remains are what we detect as radiofossils.
Abel 3266
Our new paperpublished in the Royal Astronomical Society Monthly Noticespresents a very detailed study of a galaxy cluster called Abell 3266.
This is a particularly dynamic and messy collision system some 800 million light-years away. It has all the features of a system that should harbor relics and halos, but until recently none had been detected.
Follow-up of the work carried out with the Murchison wide field array earlier this yearWe use new data from ASKAP radio telescope and the Australia’s Compact Telescope Array (ATCA) to see Abell 3266 in more detail.
Our data paints a complex picture. You can see this in the main image: the yellow colors show features where the power input is active. The blue haze represents the hot plasma, captured at X-ray wavelengths.
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 visible in red near the bottom of the image (see below for a zoom). And our data here reveals particular characteristics that have never been seen before in a relic.
(Christopher Riseley, using data from ASKAP, ATCA, XMM-Newton, and the Dark Energy Survey)
Above: The ‘wrong path’ relic in Abell 3266 is shown here with the yellow/orange/red colors representing the glow of the radio.
Its concave shape is also unusual, earning it the catchy nickname of a “wrong way” relic. Overall, our data breaks our understanding of how relics are generated, and we’re still working to decipher the complex physics behind these radio objects.
Ancient remains of a supermassive black hole
The radiofossil, seen towards the top right of the main image (and also below), is very faint and red, indicating that it is ancient. We believe that this radio emission came from the galaxy in the lower left, with a central black hole that has been off for a long time.
(Christopher Riseley, using data from ASKAP, ATCA, XMM-Newton, and the Dark Energy Survey)
Above: The radium fossil in Abell 3266 is shown here with red colors and outlines representing the radium brightness measured by ASKAP, and blue colors showing hot plasma. The cyan arrow points to the galaxy that we believe was once fueled by the fossil.
Our best physical models just don’t fit the data. This reveals gaps in our understanding of how these sources evolve, gaps that we are working to fill.
Finally, using a clever algorithm, we defocused the main image to look for a very faint emission that is invisible at high resolution, uncovering the first detection of a radio halo in Abell 3266 (see below).
(Christopher Riseley, using data from ASKAP, ATCA, XMM-Newton, and the Dark Energy Survey)
Above: 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 the hot plasma. The dashed cyan curve marks the outer limits of the radio halo.
Towards the future
This is the beginning of the road to understanding Abell 3266. We have discovered a lot of new and detailed information, but our study has raised even more questions.
The telescopes we use are laying the groundwork for revolutionary science from the square kilometer matrix Project. Studies like ours allow astronomers to discover what we don’t know, but you can be sure that we will discover it.
We recognize the Gomeroi 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 the ASKAP and Murchison Widefield Array are located. 
Christopher RiseleyResearch Fellow, University of Bologna Y Tessa Vernstromexperienced Research Fellow, The University of Western Australia.
This article is republished from The conversation under a Creative Commons license. Read the Original article.
