Observing the universe with radio telescopes has revealed many oddities over the decades. From pulsars to fast-radio bursts, the universe is full of peculiar objects. One particular funky structure is the so-called Odd Radio Circles (ORCs). They are about a million light-years across and yet they are very faint and difficult to see.

New observations have delivered new details about these ORCs. There are five known ORCs and the team focused on one in particular, called ORC1C. The observations, reported in the Monthly Notices of the Royal Astronomical Society, showed that these shells are created by radiation from accelerated electrons, and they have a complex internal structure made of multiple arcs. 

“People often want to explain their observations and show that it aligns with our best knowledge. To me, it’s much more exciting to discover something new, that defies our current understanding,” co-author Dr Jordan Collier of the Inter-University Institute for Data Intensive Astronomy, said in a statement.

Based on the observations, the team has three potential explanations for what is creating these ORCs. Their formation could be related to the collision of two supermassive black holes at the center of the elliptical galaxy enclosed within ORC1C.

Another possibility is that the supermassive black hole was actively creating a jet of material in the past. The ORC would be the remains of that seen by staring down in the direction of the jet. The last scenario is that the galaxy experienced a starburst, a dramatic increase in star formation, which generated powerful winds of charged particles.

Models of these scenarios can’t explain everything that is seen in space, but currently, the starburst hypothesis is the one that fits the data a bit better than the others.

“We know ORCs are rings of faint radio emissions surrounding a galaxy with a highly active black hole at its centre, but we don’t yet know what causes them, or why they are so rare,” lead author Professor Ray Norris said.

The observations were possible with the two precursor observatories of the Square Kilometer Array (SKA): ASKAP, located on Wajarri Yamatji country in Western Australia, and MeerKAT, located in the Northern Cape province of South Africa. Using both has revealed new details of these structures and suggests just how much more of the universe we will see once SKA comes online in 2027.

“Nearly all astronomy projects are made better by international collaboration – both with the teams of people involved and the technology available,” Professor Elaine Sadler, Chief Scientist of CSIRO’s Australia Telescope National Facility said.

“ASKAP and MeerKAT are both precursors to the international SKA project. Our developing understanding of odd radio circles is enabled by these complementary telescopes working together.”