Mysterious astronomical objects, so-called strange radio circles, or ORCs, have been carefully studied by an international team of astronomers using the world’s most powerful radio telescopes. The nature of the “orcs” is still mysterious, but new data from the South African telescope MeerKAT allows us to get closer to solving this mystery.
The South African radio telescope MeerKAT received a detailed image of one of the most mysterious space objects – the so-called strange radio circles, or “orcs” – ORCs – Odd Radio Circles. For the first time, these radio circles were discovered in 2019 by the Australian radio telescope ASKAP – Australian Square Kilometer Array Pathfinder. So far, ORCs have been detected only exclusively in the radio range, and optical, infrared and X-ray telescopes do not see them. An article by an international group of astronomers about the “orks” was published in the Monthly Notices of the Royal Astronomical Society.
A new detailed image taken by the South African Radio Astronomy Observatory’s MeerKAT radio telescope gives researchers more room to narrow down the range of pertinent theories that describe the cause of these phenomena.
Currently, there are several leading theories explaining the reasons for the emergence of ORCs. They may be traces of some gigantic cataclysm in the center of the parent galaxy – like the merger of two supermassive black holes or the absorption of a large amount of matter by this black hole. It could also just be the result of the more or less normal activity of a supermassive black hole spewing out two jets from its poles, relativistic jets of high-energy charged particles crashing into the surrounding gas. Finally, ORCs may be the result of the “finishing blow” of active star formation – a shock wave propagated as a result of the formation of many stars in the galaxy.
Jordan Collier of the data-intensive Intercollegiate Astronomy Center, which compiled the image from the MeerKAT data, said that continuing to observe these strange radio circles will give researchers more clues.
There is often a tendency among researchers to immediately explain all their observations and show that they are consistent with the most authoritative theories. However, it is much more interesting to discover something new that challenges our current level of knowledge.
The dimensions of the radio rings are amazing – their diameter is at least a million light-years, which is 16 times the size of the Milky Way. Despite this, the fuzzy contours of the radio circles are very difficult to distinguish. Professor Ray Norris of the University of Western Sydney in Australia, lead author of the paper, says only five such rings have been found in the entire cosmos so far. “We know that ORCs are rings of weak radio emission surrounding galaxies with highly active supermassive black holes at their centers, but we still don’t know exactly what causes them to appear and why they remain so rare,” he said.
The ORC image taken by the MeerKAT radio telescope resembles a blurry blue-green jellyfish pulsing in the vast ocean of space, but, of course, the “colors” chosen to visualize this object are just a tribute to the conventions of human perception.
“Now we have beautiful images of one of these rings taken with the South African radio telescope, which show the ORC in stunning detail,” Norris wrote in a special column for The Conversation. “For example, MeerKAT sees a small spot of radio emission in the center of the ring, which coincides with a distant galaxy. Now we are almost sure that this galaxy gave rise to the ORC. We see these central galaxies in the case of other ORCs located at great distances from the Earth. Now we understand that these rings surround distant galaxies that are about a billion light years away, which means that the rings are huge – they are about a million light years across.
In fact, the “rings” with bright edges are only the outlines of spherical shells surrounding the galaxies, like a blast wave from a long-standing galactic cataclysm. They look like rings instead of balls, only because they are almost transparent, and at the edges, where the eye meets more material, they appear denser – it turns out something like an uneven soap bubble.
“One of the biggest surprises in the MeerKAT data was that inside the ring we saw several curved filaments of radio emission. So far, we have not figured out what it is. But we do know that the sphere is so huge that it swallowed other galaxies as it expanded from the central galaxy. Perhaps the filaments are traces of gas torn off from other galaxies by a shock wave passing through them? asks Norris.
Professor Elaine Sadler, Chief Scientist at CSIRO, Australia, which operates the ASKAP radio telescope, said ASKAP and MeerKAT are now working together to find and describe these objects as efficiently as possible. “Almost all astronomical projects are taken to the next level by international collaboration, both in the people involved and in the technology available,” said Professor Sadler. – ASKAP and MeerKAT in the future will become part of the world’s largest international radio interferometer SKA – Square Kilometer Array. Our ever-expanding knowledge of the peculiarities of the structure of strange radio circles will be reinforced by the joint work of these complementary telescopes.”
Undoubtedly, the SKA radio interferometer will detect many more new ORCs in the future, and then we will be able to learn more about the life cycle of galaxies. But until the SKA is up and running, ASKAP and MeerKAT will remain at the forefront of exploring the mysteries of the universe.
To uncover all the secrets of strange radio circles, scientists will need access to even more sensitive radio telescopes, which is exactly what the SKA project will provide, which will also include instruments from other countries: Great Britain, France, Canada, China and India.