An odd radio circle studied with the MeerKAT radio telescope

ORC1 seen by MeerKAT and in the background optical data from the Dark Energy Survey (Image J. English (U. Manitoba)/EMU/MeerKAT/DES(CTIO))
ORC1 seen by MeerKAT and in the background optical data from the Dark Energy Survey (Image J. English (U. Manitoba)/EMU/MeerKAT/DES(CTIO))

An article published in the journal “Monthly Notices of the Royal Astronomical Society” reports a study based on a new image of a so-called odd radio circle (ORC). A team of researchers used the MeerKAT radio telescope to observe this structure with a diameter of over one million light-years visible only at radio waves. Each new observation of this type of phenomenon offers new information, as only five of them are known at the moment. The information collected with MeerKAT could help verify the theories that were proposed and reach a reasonably certain explanation for its origin and nature.

The first odd radio circle was discovered in 2019 during observations conducted with ASKAP, another of the radio telescopes precursors of SKA, the next-generation radio telescope. Astronomer Anna Kapinska was directing the EMU (Evolutionary Map of the Universe) survey, which recently published the first results, which include the discovery of various phenomena including odd radio circles.

The circular shape, the truly enormous extension that reaches around a million light-years, and the greater brightness along the edges stimulated the curiosity of astronomers. Various theories have been proposed but none can fully explain the odd radio circles, so the observations of the known ones and the search for more continued. Attempts have been made to observe these phenomena in other bands of the electromagnetic spectrum as well but they’re visible only at radio waves.

The MeerKAT radio telescope was used to observe the odd radio circle cataloged as ORC1. The bottom image (Courtesy EMU team using data from ASKAP and MeerKAT radio telescopes) shows on the left the image of ORC1 captured by ASKAP at 944 MHz and on the right the new image captured by MeerKAT at 1,284 MHz.

The two radio telescopes are used to develop different technologies that will be implemented in SKA and have different characteristics. ASKAP is ideal for observing large areas of the sky, also to discover rare objects and phenomena such as odd radio circles. MeerKAT, on the other hand, is ideal for follow-up studies that examine those objects and phenomena in greater detail. That’s why the ORC1 image captured with MeerKAT is more detailed than the one captured with ASKAP.

There are currently three main theories on the origin of odd radio circles: they might be remnants of a large explosion at the center of a galaxy such as the merger of two supermassive black holes, they might be powerful jets of energetic particles that escape from the center of a galaxy or they might be the product of shock waves generated by starburst activity in a galaxy.

These theories are all linked to phenomena related to the central areas of galaxies with active supermassive black holes but five odd radio circles are very few to find patterns. The link with black holes could be direct or indirect, as they can influence star formation in a galaxy.

According to Professor Ray Norris, the first author of this study, SKA will allow discovering many other odd radio circles and will be able to tell us more about the life cycles of galaxies. It’s a case in which we can expect a new instrument to help solve a scientific mystery. Its precursors are already showing the potential of SKA with the discovery of this mystery and the first investigations. Odd radio circles are only one of the many cosmological phenomena that will be investigated with the SKA radio telescope.

ORC1 seen by ASKAP and MeerKAT

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