May 25, 2022

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Mysterious ORCs shine in their best (but still mysterious) shots yet

‘Unusual radio circuits’ were first observed in space in 2019, making them one of the latest mysteries the universe presents to us. But astronomers won’t let her go.

In 2019, while working with Australian SKA Pathfinder Telescope About a strange phenomenon, a radio radiation ring. Astronomers have never seen anything like it before, and been completely unable to detect it. The latter is also evident from the name they came up with for this mysterious phenomenon: ORC. this means strange radio circuitor an unusual radio circuit.

Five ORCs
We are now three years later and we are aware of five circuits of radioactive radiation. He points out that ORCs are so rare, that they have been thoroughly and extensively researched in recent years, but without much success. However, it should be noted that it is very difficult to see ORCs using conventional radio telescopes; It doesn’t emit much radio emissions, so very powerful telescopes are needed to see it at all.

spherical
Of course, in recent years, astronomers have also puzzled over how these mysterious radio circuits form. And now they have ideas about it. For example, follow-up research has shown that some ORCs have discovered distant galaxies surrounding them. Moreover, perhaps they are not circles in the strict sense of the word, but have a spherical shape. This field can be up to a million light-years wide, and therefore houses a galaxy. It is therefore suspected that these central galaxies somehow generate radio emissions.

new notes
Astronomers are determined to solve the mystery of the ORCs. So take a closer look at the first discovered ORC. They used the MeerKAT radio telescope. Where ASKAP is particularly good at surveying large parts of the universe, MeerKAT is particularly well suited to magnifying certain parts of it. And for the new study, the scientists directed the powerful radio telescope into an unusual radio circuit. It yields the best recordings we have of these mysterious phenomena and also reveals something new.

On the left is the ASKAP note that led to the discovery of ORCs. On the right is a more detailed MeerKAT note on the first ORC. Photo: EMU/ASKAP/MeerKAT.

New information
For example, MeerKAT recordings show that radio-radiation arcs can be found in unusual radio circuits. Researchers say they may have been on the heels of other galaxies that have traveled through the ORC. This hypothesis is supported by the fact that scientists can also show that the ORC is located in a fairly densely populated region: near the galaxy that is in the heart of the ORC, many galaxies can be seen and some of them are even in the ORC. If, as most researchers believe, the unusual radio circuit originated from certain developments in the galaxy that lie at the heart of most ORCs and were gradually expanded, then that ORC would be doomed to encounter nearby galaxies and thus affected (and thus perturbed).

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This artistic impression shows how radio circles see daylight after an explosion in the center of the galaxy. The circles – which are 16 times the size of our Milky Way – are thought to have taken a billion years to reach their current size, passing through other nearby galaxies as well. Photo: Sam Moorfield/CSIRO.

polarization
In addition, the researchers succeeded for the first time in measuring the polarization of the radio signal of the ORC Resource Center. And this is important, because this polarization can tell us more about the presence and shape of magnetic fields. In this case, the polarization of the radio signal shows that the edge of the circuit in particular has a relatively strong magnetic field.

Electrons
Finally, the observations also show that the radio radiation is caused by electrons racing along a magnetic field at nearly the speed of light. This is an interesting discovery. Because there are not many processes that can move electrons to such a high speed. Based on the latest observations, the researchers say there are only three possible explanations for the origin of the mysterious ORCs.

One
For example, the unusual radio circuit may be the remnant of a massive explosion – for example, due to the merging of two supermassive heavy holes – in the center of the galaxy. In this scenario, you would expect to find an active galactic nucleus at the galactic core today. And that is certainly the case with the three ORCs that we know for sure harbor a galaxy in their hearts. So this is a real hypothesis.

This image combines data from the MeerKAT radio telescope with optical and near-infrared data from the Dark Energy Survey. Photo: J. English (U. Manitoba) / EMU / MeerKAT / DES (CTIO).

two
But there are two others. For example, researchers point out that galaxies—when you study them at radio wavelengths—often feature two outflowing currents rushing in opposite directions from the galactic center. When you look at the side of such a galaxy, those jet streams – in the form of two lobe-like structures – are often very visible. But suppose we admire these galaxies not from the side, but from above or from below. In this case, those lobe-like structures can suddenly become ORC-like. It’s an interesting hypothesis, but not exactly the best one. Because if ORCs were disguised jet streams, you would expect them not to be as rare as currently believed. In addition, the researchers noted that lobe-like structures often have an irregular shape, and therefore cannot easily assume a nearly perfect spherical shape, even when viewed from above. However, this hypothesis cannot be categorically rejected at this point either, so this interpretation of ORCs remains contested for the time being.

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three
The third and final explanation is starburst termination shock† This creates a shock wave due to star formation. This hypothesis is supported by the fact that many new stars have already formed long ago in the galaxy in the heart of the ORC under investigation. In addition, the distance between this shock wave and the central galaxy corresponds to the estimated size of the unusual radio circuit.

It is not possible to say with certainty on the basis of the new observations which of these three interpretations is correct. So more research is urgently needed. During this follow-up investigation, the first thing that matters is the discovery of more ORCs. In this way it is possible to determine what characteristics they have in common and it is important to be able to know exactly how they appear. Now, spotting ORCs is easier said than done, researchers have discovered in recent years. But there is hope. For example, there are high expectations regarding square kilometer array to be set up in South Africa (in which the Dutch government has also invested heavily). This radio telescope is still under construction, but should be able to make the first observations in the coming years. “When completed, the SKA telescope will undoubtedly discover more ORCs and tell us more about the life cycle of galaxies,” said study researcher Ray Norris. But in the meantime, astronomers are sure not sitting still; There may still be a lot to discover with ASKAP and MeerKAT.