Your name says it all. Odd Radio Circles (ORCs) have been astronomy’s most mysterious objects for a number of years, and in case you haven’t guessed it, scientists remain baffled as to exactly what these giant radio rings in space really are.
That’s despite the fact that an international team of astronomers used the MeerKAT radio telescope in South Africa – one of the most powerful radio telescopes in the world – to get the clearest image yet of the first ORC ever found, nicknamed “ORC1”. The pictures were published last week in Monthly Bulletins of the Royal Astronomical Society.
Here’s everything you need to know about ORCs – what they are, where they come from and how they can (and can’t) be explained:
What are “odd radio circles”?
They are incredibly large but faint, diffuse rings of radio emission around distant galaxies that astronomers have no explanation for. They are blue-green in color, lighter at their edges, and look a bit like smoke rings.
ORCs have so far only been detected with radio telescopes. When astronomers have optical, infrared, and X-ray telescopes pointed at them, they see nothing.
However, three of the ORCs found so far are in the vicinity of galaxies, suggesting a connection. ORCS are also called “ring galaxies”.
“We know that ORCs are rings of faint radio emissions surrounding a galaxy with a highly active black hole at its center, but we don’t yet know what causes them or why they are so rare,” said Professor Ray Norris of Western Sydney University and CSIRO and one of the authors of the paper. He has previously estimated that there are 1,000 ORCs in the night sky just waiting to be found.
The new images of the very first ORCs reveal a complex internal structure made up of multiple arcs.
What is radio astronomy?
Radio astronomy is the study of the night sky at radio frequencies. Radio telescopes detect and amplify radio waves from space — electromagnetic radiation emitted by stars, galaxies, and other cosmic objects.
How big are “odd radio circles” and how many were found?
About a million light years across. That’s 16 times larger than our own galaxy, the Milky Way. The rings are so large that they have expanded beyond other galaxies.
Astronomers believe ORCS will likely take about a billion years to reach the size we see today.
Only five odd radio circuits have ever been discovered in space. The first was discovered in 2019 using the Australian Square Kilometer Array Pathfinder radio telescope array.
Are ORCs actually wormholes through time?
The idea that ORCs could be the “throats of wormholes” was one of the ideas put forward by two Russian scientists. A wormhole is a theoretical passage through space-time connecting two physically very distant locations.
“People often want to explain their observations and show that they agree with the best of our knowledge,” said Dr. Jordan Collier of the Inter-University Institute for Data Intensive Astronomy, who compiled the image from MeerKAT data. “For me, it’s much more exciting to discover something new that defies our current understanding.”
What else could ORCs be caused by?
Could ORCs be caused by galactic spherical shock waves? Or the result of giant black holes? Could be. ORCs could signal momentous events in galactic evolution. Or not. The scientists who just imaged the first ORC have a few theories about its origin:
- They are the remnants of a massive explosion at the center of their host galaxy, like the merger of two supermassive black holes.
- They are powerful jets of energetic particles ejected from the center of a galaxy.
- They are the result of a starburst “termination shock” from the production of stars in the galaxy.
When will the mystery of the ORCs be solved?
That’s unclear, but more sensitive radio telescopes are needed to really understand ORCs. Cue Square Kilometer Array (SKAO), a $2.2 billion radio telescope like never before built that will include two large and complex radio telescope networks – 197 radio dishes in Karoo in South Africa’s Northern Cape and 131,072 antennas in Murchison deep in the outback of Western Australia.
“There is no doubt that the SKA telescopes, once built, will be able to find many more ORCs and tell us more about the life cycle of galaxies,” said Professor Norris.
I wish you clear skies and big eyes.