Astronomers Uncover a New ‘Odd Radio Circle’ Near the Heart of Our Galaxy

A mysterious ring invisible at all wavelengths except radio could be a trace of a dramatically unstable star shedding its skin.

A new radio ring may have been generated from a super giant star releasing its atmosphere through a blast of radiation, suggest astronomers from the South African MeerKAT radio telescope.

Australian astronomers using the Australian Square Kilometer Array Pathfinder telescope (ASKAP) in 2019 classified a number of strange rings of radio brightness. Lacking other attributes, such as visibility at other wavelengths, and an apparent source, these rings were named odd radio circles (ORC).

Only a few ORCs have been noted to-date, however, recently a new one has being discovered and it was said to upset the trends.

ASKAP is the technological predecessor for Zone, the Square Kilometer Array (SKA), which is a radio dish and multantenna system planned for Australia and South Africa. As befits the story, South Africa sports its own SKA precursor in the MeerKAT observatory formerly called the Karou Radio Telescope situated in the Meerkat National Park.

In the first week of November 2022 during observing with the MeerKAT telescope, an astronomer Cristobal Bordiu, the head of Catania Observatory, Italy noticed something strange. They come across an ORC that is in a place that it usually is not usually found.

Before then, all the discovered ORCs had been at high galactic latitudes, well above the Milky Way plane, thus hinting that they were either proximal to within the Milky Way or in other galaxies. Som NGCs also have a galaxy at their core that scientists believe has been formed during an outburst, for instance starburst in which multiple supernovae occur or through the merging of two supermassive black holes which also results in a burst.

However, this newly discovered ORC lies at six degrees above the galactic plane and thus seems to be a part of Milky Way if seen from the Earth. It also appears to lie toward the galactic core region, however this might not be soจร it could be much closer or farther from the core than 26000 light years.

The ORC is listed as J1802–3353 and named Kýklos by its discoverers, who took the Greek meanings circulus or circle; it measures 80 arcseconds in diameter across the sky. The ring is detectable only at radio wavelengths, and it is very faint, and clumpy and only 6 arcseconds in thickness, making it nearly circular. What is less expected is that it has relatively flat radio spectrum with no clear lines previously seen in earlier ORCs.

Bordiu’s team understood that this could be something completely different, but, before implementing this ORC, it was necessary to eliminate other options.

According to Gaia mission of European Space Agency there are three galaxies located in area of Kýklos in the sky. Of these galaxies, one is only 3 arcseconds away from the galactic centre of the ring. However if Kýklos was born out of this galaxy itself then the reason for the flatter spectrum to other ORCs associated with galaxies cannot be explained well.

Thus, if Kýklos is not extragalactic then it must be local and situated inside our galaxy, milky way, hence a stellar source. Supernova remnants, for example, round nebular structures made by an explode of a supernova and a shock wave affecting the interstellar medium gas and dust, might be possible candidates.

However, supernova remnants normally produce X-rays and, to date, no X-rays have been unveiled emanating from Kýklos. While a few other objects: pulsars (rotating neutron stars in some of which form from supernovas) can be seen within the ring as seen from the Earth, we have no information of how far they are located, which makes it impossible for scientists to know if the pulsars are in any way connected to the ring, or used in the ring only by chance.

There is one other possibility that might makes sense: that what we’re seeing is Kýklos as a planetary nebula— what’s left when a star like our own someday sheds its outer layers. Average size of planetary nebulas is about 3 light years in diameter and since Kýklos is not a planetary nebula it must be quite large or situated fairly close to us in order to be as wide as 80 arcseconds. For comparison’s sake, the well-known Ring Nebula found in the constellation of Lyra measures 230 arcseconds in size and is 2,200 light-years away. Nevertheless, planetary nebulas do produce light particularly in the hydrogen-alpha collection but till date no such emission is seen from Kýklos.

Perhaps, it was formed by an enormous Wolf–Rayet star which is in a state of instability. These stars have the potential of emitting high energy radiation winds that can sweep away their extensive atmospheres thus causing them to decrease in mass, which makes them to become stable. Wolf–Rayet stars are named either after the associated nebulae or by the after shedding the outer hydrogen layer; one can see heavier elements inside such a star, for example, helium and oxygen.

However, no Wolf–Rayet nebula is observed in Kýklos, but this might be a problem because the radiation wind from Wolf–Rayet star is capable of devastating neighboring dusty nebulae fast. At 24 microns, only cooler dust farther out would survive and radiate, but there exist no data showing the existence of such dust. Still, the flat spectrum detected in Kýklos corresponds to the spectrum that is obtained from Wolf–Rayet stars in the process of stellar wind.

According to the available data for the present time, the morphological and spectral characteristics Kýklos look similar to a Wolf–Rayet shell, Continued Bordiu’s team.

Althrough there is no officially classified Wolf–Rayet star within Kýklos’ perimeter one bright star that can be found there is not a Wolf–Rayet star: HD 164455. Three other stellar candidates have been listed by Gaia; They include a bluish star which is about twenty-four thousand, five hundred light years from earth. If this star is the source of Kýklos the ring would measure approximately 10 light years in diameter at that distance. Nevertheless, no spectral information that would indicate whether this star is a Wolf–Rayet star is available.

The last step will then be to feed the data collected by the James Webb Space Telescope into the system and possibly shed light on Kýklos.