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In September 2019, my colleague Anna Kapinska gave a presentation showing some interesting objects she had found while browsing our new radio astronomical data. She had started noticing very strange shapes that she couldn’t easily adapt to any type of known object.
Among them, labeled by Anna as WTF?, was the image of a ghostly circle of radio transmissions, suspended in space like a ring of cosmic smoke.
Neither of us had seen anything like it before, and we had no idea what it was. A few days later, our colleague Emil Lenc found a second one, even more frightening than Anna’s.
Anna and Emil had reviewed the new images from our pilot observations for the Evolutionary Map of the Universe (EMU) project, carried out with CSIRO’s revolutionary new Australian Square Kilometer Array Pathfinder (ASKAP) telescope.
EMU plans to boldly probe parts of the Universe where no telescope has gone before. It can do this because ASKAP can monitor large parts of the sky very quickly, probing to depths previously only reached in tiny areas of the sky, and being particularly sensitive to faint and diffuse objects like these.
I predicted a few years ago that this exploration of the unknown would likely make some unexpected discoveries, which I called WTF. But neither of us expected to find something so unexpected, so quickly.
Due to the huge volumes of data, I expected the discoveries to be made using machine learning. But these discoveries were made with an old-fashioned good eye.
Hunting ORC
Our team searched the rest of the data with the naked eye, and we found some of the mysterious round blobs. We called them ORC, which means “strange radio circles”.
But the big question, of course, is, “what are they?”
At first we suspected an imaging artifact, possibly generated by a software error. But we quickly confirmed that they were real, using other radio telescopes. We still have no idea their size or distance.
They could be objects in our galaxy, maybe a few light years across, or they could be far away in the Universe and maybe millions of light years across.
When we look at images taken with optical telescopes at the position of the ORCs, we do not see anything. Radio emission rings are likely caused by clouds of electrons, but why can’t we see anything in the visible wavelengths of light?
We don’t know, but finding a puzzle like this is every astronomer’s dream.
We know what they are not
We have ruled out several possibilities for what CROs might be.
Could they be supernova remnants, the clouds of debris left behind when a star in our galaxy explodes? No. They are far from most stars in the Milky Way and there are too many of them.
Could they be the radio emission rings that we sometimes see in galaxies undergoing intense star-forming bursts? Again, no. We don’t see any underlying galaxy that would host star formation.
Could they be the giant radio emission lobes we see in radio galaxies, caused by jets of electrons bursting from the surroundings of a supermassive black hole? Unlikely, as ORCs are very distinctly circular, unlike the tangled clouds we see in radio galaxies.
Could they be Einstein’s rings, in which radio waves from a distant galaxy are bent in a circle by the gravitational field of a cluster of galaxies? Always not. The ORCs are too symmetrical and we don’t see any clusters in their center.
A real mystery
In our article on CROs, to appear in the Astronomical Society of Australia Publications, we go through all the possibilities and conclude that these enigmatic blobs are unlike anything we already know.
So we have to explore things that might exist but have not yet been observed, like a vast shock wave caused by an explosion in a distant galaxy. Such explosions may have something to do with rapid radio bursts or collisions of neutron stars and black holes that generate gravitational waves.
Or maybe they are something else entirely. Two Russian scientists have even suggested that ORCs could be the “throats” of wormholes in space-time.
Based on the handful that we have found so far, we estimate that there are about 1,000 ORCs in the sky. My colleague Bärbel Koribalski notes that research is now underway, with telescopes around the world, to find more ORCs and understand their cause.
This is delicate work, as ORCs are very weak and hard to find. Our team brainstorm all of these ideas and more, hoping for the eureka moment when one of us, or maybe someone else, suddenly has the flash of inspiration that solves the puzzle.
It is an exciting time for us. Most astronomical research is aimed at refining our knowledge of the Universe or testing theories. Very rarely do we have the challenge of stumbling across a new type of object that no one has seen before and trying to figure out what it is.
Is this a completely new phenomenon, or something we already know but view in a strange way? And if it’s really completely new, how does it change our understanding of the Universe? Watch this place!
Ray Norris, Professor, School of Science, Western Sydney University.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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