In 2020, Dr. Ray Norris and his team conducted radio observations of the sky using the Australian Square Kilometre Array Pathfinder telescope. They found a few extended mysterious structures, some of which are larger than our galaxy. Usually, extended structures in the sky are the remnants of the explosive deaths of stars. These are generally visible throughout the electromagnetic spectrum, i.e., also seen through X-ray, optical, and infrared telescopes..
However, these radio structures were not visible in any of these regimes. Due to their unknown nature and almost circular shape, these researchers termed these objects Odd Radio Circles, or ORCs. A more recent study by the same research team used a better-resolution radio telescope called MEERKaT to study one of these ORCs. This work shed some light on the possible origin(s) of these ORCs. They hypothesized three possible scenarios as follows:
- Remains of Supermassive black holes merging event: ORCs could be remnants of a huge explosion followed by the merging of two supermassive black holes at the center of a galaxy.
- Radio lobes side view from an active galactic nucleus: An active galactic nucleus (AGN) is a supermassive black hole with jets coming out in opposite directions. These jets are seen by radio telescopes. If one of these jets' direction is facing the Earth, one would see a big extended structure like ORCs.
- Starburst termination shock: Rapid star formation could launch winds at a significant distance from the galaxy's center that would travel at relatively high speeds, almost like a shock wave. This wind expanding in a nearly spherical shape would be visible via radio telescopes.
These researchers argued that none of these three scenarios works better than the other when applied to the current data. Therefore, to understand the true nature of this ORC puzzle, more sensitive radio observations and possibly more ORCs are needed.
Source: Monthly Notices of the Royal Astronomical Society, Nature news