The universe is littered with universe clusters – huge structures piled up at the intersections of the cosmic web (opens in new tab). A single cluster can span millions of light-years across and consists of hundreds or even thousands of galaxies.
However, these galaxies represent only a few percent of a cluster’s total mass. About 80% of that is dark matterand the rest is a hot plasma “soup”: gas heated to above 10,000,000 degrees Celsius and intertwined with weak magnetic fields.
We and our international team of colleagues have identified a series of rarely observed radio objects – a radio relic, a radio halo and fossil radio emission – in a particularly dynamic galaxy cluster called Abell 3266. They defy existing theories about both the origin of such objects and their origins. characteristics.
Relics, Halos and Fossils
galaxy clusters allow us to study a wide variety of rich processes – including magnetism and plasma physics – in environments we can’t mimic in our labs.
When clusters collide, huge amounts of energy are put into the particles of the hot plasma, generating radio emissions. And this emission comes in different shapes and sizes.
“Radio relics” are an example. They are arcuate and sit toward the edge of a cluster, propelled by shock waves traveling through the plasma, causing a jump in density or pressure and energize the particles. An example of a shock wave on Soil is the sonic boom that occurs when an aircraft breaks the sound barrier.
“Radio halos” are irregular sources that lie toward 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 generated by collisions between galaxy clusters — but many of their rugged details remain elusive.
Then there are “fossil” radio sources. These are the radio remnants of the death of a supermassive black hole at the center of a radio galaxy.
When in action, black holes shoot huge jets of plasma (opens in new tab) far beyond the galaxy itself. When they run out of fuel and stop, the jets start to disappear. The remains are what we detect as radiofossils.
U.S new paper (opens in new tab)published in the Monthly Notices of the Royal Astronomical Society, presents a very detailed study of a galaxy cluster called Abell 3266.
This is a very dynamic and messy colliding system about 800 million light-years away. It has all the features of a system that: should host relics and halos – but none had been discovered until recently.
Follow-up of work performed using the Murchison Widefield Array (opens in new tab) earlier this year (opens in new tab)we used new data from the ASKAP radio telescope (opens in new tab) and the Australia Telescope Compact Array (opens in new tab) (ATCA) to see Abell 3266 in more detail.
Our data paints a complex picture. You can see this in the lead image: yellow colors show features where energy 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’ve lost a lot of energy over time, or they’ve never had much to begin with.
The radio relic is visible in red at the bottom of the image (see below for a zoom). And our data here reveals specific features never seen before in a relic.
Its concave shape is also unusual, giving it the catchy nickname of a “wrong” relic. Overall, our data is breaking 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 in the top right corner of the image (and also below), is very faint and red, indicating it is old. We think this radio emission originally came from the lower left galaxy, with a central black hole that has long been turned off.
Our best physical models just don’t fit the data. This reveals gaps in our understanding of how these resources evolve — gaps we’re trying to fill.
Finally, using a clever algorithm, we defocused the main image to look for very faint emission that are invisible at high resolution, unearthing the first detection of a radio halo in Abell 3266 (see below).
On the way to the future
This is the beginning of the road to understanding Abell 3266. We have uncovered a wealth of new and detailed information, but our research has raised even more questions.
The telescopes we have used lay the foundation for revolutionary science from the Square kilometer array (opens in new tab) project. Studies like ours allow astronomers to find out what we don’t know — but rest assured we will find out.
We recognize 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 Radioastronomy Observatory site, where ASKAP and the Murchison Widefield Array are located.
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