The recently discovered spectral circles in the sky cannot be explained by current theories and astronomers are thrilled

In September 2019, my colleague Anna Kapinska gave a presentation showing interesting objects she had found while navigating our new radio astronomy data. He had begun to notice very strange shapes that he couldn’t easily adapt to any known type of object.

Among them, Anna labeled as WTF?, was the image of a ghostly circle of radio emissions, suspended in space like a cosmic smoke ring. Neither of us had ever 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 disturbing than Anna’s.

Anna and Emil were examining new images from our pilot observations for the Evolutionary Map of the Universe (EMU) project, made with CSIRO’s revolutionary new Australian Square Kilometer Array Pathfinder (ASKAP) telescope.

The EMU plans to boldly probe parts of the Universe where no telescope has gone before. It can do this because ASKAP can detect large swaths of the sky very quickly, probing to a depth previously reached only in tiny areas of the sky and being particularly sensitive to faint and diffuse objects such as these.

I predicted a couple of years ago this exploration of the unknown would probably make unexpected discoveries, which I called WTF. But none of us expected to discover 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 a good old-fashioned look.

Read more: expect the unexpected from the big data boom in radio astronomy

ORC hunting

Our team searched the rest of the data by eye and we found some other mysterious round blobs. We dubbed them ORC, which stands for “strange radio circles”. But the big question, of course, is “what am I?”

We initially suspected an image artifact, possibly generated by a software error. But we soon confirmed that they are real, using other radio telescopes. We still have no idea how big or how far away they are. They could be objects in our galaxy, perhaps a few light years in diameter, or they could be distant in the Universe and perhaps millions of light years in diameter.

When we look into the images taken with optical telescopes in the position of the ORCs, we see nothing. The radio emission rings are likely caused by electron clouds, but why don’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.

Read more: The Australian Square Kilometer Array Pathfinder finally reaches the big data highway

We know what they are not

We have ruled out several possibilities for what ORCs might be.

Could it be the supernova remnants, the clouds of debris left behind when a star in our galaxy explodes? No. They are far from most of the stars in the Milky Way and there are too many.

Could it be the radio emission rings sometimes seen in galaxies that undergo intense bursts of star formation? Again, no. We don’t see any underlying galaxy that will host star formation.

Could it be the giant lobes of radio emission we see in radio galaxies, caused by jets of electrons splashing out of the environment of a supermassive black hole? Not likely, because ORCs are 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 into a circle by the gravitational field of a cluster of galaxies? Not yet. ORCs are too symmetrical and we don’t see a cluster in their center.

A real mystery

In our article on ORCs, which is coming out in the Astronomical Society of Australia Publications, we look at all the possibilities and conclude that these enigmatic blobs look like nothing we already know about.

So we need to explore things that may exist but have not yet been observed, such as a vast shockwave from an explosion in a distant galaxy. Such explosions may have something to do with fast radio bursts or with collisions between neutron stars and black holes that generate gravitational waves.

Read more: How we approached the location of a fast radio blast in a distant galaxy far away

Or maybe they are something else entirely. Two Russian scientists have even suggested that ORCs may be wormhole “throats” in spacetime.

From the handful we’ve found so far, we estimate there are around 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.

It’s a complicated job, because ORCs are very weak and hard to find. Our team is brainstorming 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 honing our knowledge of the Universe or testing theories. Very rarely do we have the challenge of stumbling upon a new type of object that no one has ever seen before and trying to understand what it is.

Is it a completely new phenomenon or something we already know but viewed in a strange way? And if it’s really completely new, how does our understanding of the Universe change? Look at this space!