They find some strange radio sources in a distant galaxy cluster: “They make us rethink what we thought we knew”
The universe is filled with galaxy clusters : gigantic structures stacked at the intersections of the cosmic web. A star cluster can span millions of light-years and be made up of hundreds, or even thousands, of galaxies.
The colliding cluster Abell 3266 as seen across the electromagnetic spectrum, using data from ASKAP and ATCA.
However, these galaxies only represent a small fraction of the total mass of the cluster. About 80% is dark matter , and the rest is a “soup” of hot plasma: gas heated to over 10,000,000 degrees Celsius and with a weak magnetic field.
We and our international team of colleagues have discovered many rarely observed radio objects—radio relics, radio coronas, and fossil radio emissions—in a particularly dynamic galaxy cluster called Abell 3266 . They ignore theory. exist in such an object. and their characteristics.
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 star clusters collide with each other, a lot of energy is deposited in the hot plasma particles, causing radio emissions. This question comes in all shapes and sizes.
Radio relics are an example. They are arc-shaped and plunge toward the outer periphery of the cluster, driven by shock waves that traverse the plasma, causing jumps 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.
“Wireless coronas” are sources of irregularities found in the centers of star clusters. They are powered by turbulence in the hot plasma, which energizes the particles. We know that both halos and remnants are created by collisions between galaxy clusters, but many of their gritty details remain elusive.
Then there are the “fossil” sources of radio. These are the radio remnants of the death of supermassive black holes at the centers of radio galaxies.
In action, the black hole spews huge jets of plasma, far beyond the Milky Way itself. When they ran out of fuel and shut down, the jets began to dissipate. The remains are the radioactive fossils we detected.
Our new paper, published in the Monthly Notices of the Royal Astronomical Society, provides a very detailed study of a galaxy cluster called Abell 3266.
The ‘wrong way’ relic on Abell 3266 is shown here with yellow/orange/red colors representing the glow of the radio.
This is a particularly dynamic and chaotic collision system some 800 million light-years away. It has all the hallmarks of a system that is supposed to carry relics and auras, but until recently it had not been found.
Building on work done with the Murchison Widefield Array earlier this year, we use new data from the ASKAP radio telescope and Australia Telescope Compact Array (ATCA) to look at Abell 3266 in more detail.
Our data paints a complex picture. You can see this in the main image: the yellow shows the function with the power input active. The blue haze represents hot plasma trapped 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. Over time, they either lose a lot of energy or don’t have much energy in the first place.
The radium fossil in Abell 3266 is shown here with red colors and outlines representing the radio glow as measured by ASKAP, and blue colors showing the hot plasma. The cyan arrow points to the galaxy we believe once fed the fossil.
The radio relic is shown in red near the bottom of the image (see enlarged below). The data we have here reveals peculiar features that have never been seen before in ruins.
Its concave shape is also unusual, earning it the attractive nickname of a “wrong way” relic. Overall, our data breaks our understanding of how relics are generated and we are still working to decipher the complex physics behind these radio objects.
Ancient remains of a supermassive black hole
The radiofossil seen from the top right (and bottom) of the main image is very faint and red, indicating that it is very old. We think this radio emission originally came from the galaxy on the lower left, with a central black hole that has been closed for a long time.
Our best physical models simply cannot fit the data. This sheds light on the gaps in our understanding of how these sources have evolved and what we are trying to fill.
The radio halo in Abell 3266 is shown here with red colors and outlines representing the radio brightness as measured by ASKAP, and blue colors showing the hot plasma. The dashed cyan curve marks the outer limits of the radio halo.
Finally, we discovered the radio corona in Abell 3266 for the first time (see below) using a clever algorithm to blur the main image to look for very faint emissions that are not visible at high resolution.
To the future
This is the beginning of the path to understanding Abell 3266. We have uncovered a lot of new and detailed information, but our research raises even more questions.
The telescopes we use are laying the groundwork for the revolutionary science of the Square Kilometer Array project (opens in new tab). Studies like ours allow astronomers to find out what we don’t know, but you can be sure we will.
We acknowledge the Gomeroi people as the traditional owners of the site where ATCA is located, 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.