There’s A Mysterious Ring Of Radio Light Near The Center Of Our Galaxy, And It Could Be A Remnant Of An Extremely Unstable Star Shedding Its Skin
Near the center of our galaxy, a mysterious ring of radio light could be a remnant of an extremely unstable star shedding its skin. Astronomers discovered it with the MeerKAT radio telescope in South Africa.
It isn’t the first time such a phenomenon has been detected. In 2019, astronomers working with the Australian Square Kilometer Array Pathfinder telescope (ASKAP) noticed multiple rings of radio light that could not be detected at any other wavelength of light. The rings had no obvious source. So, they were referred to as “odd radio circles” or ORCs.
Currently, astronomers only know of a handful that exists. But, the most recently discovered ORC defies explanation.
In November 2022, a team of astronomers led by Cristobal Bordiu from Catania Observatory in Italy spotted an ORC while making observations with MeerKAT. However, the ORC was not where it was supposed to be.
Previously, all ORCs were located at high galactic latitudes, meaning that they were way above the plane of our galaxy, the Milky Way.
So, they were either very close to us, or they were extragalactic. Several ORCs actually contained a galaxy in the middle of their rings.
Those ORCs were thought to have been created by an event involving lots of supernovas or a merger between two supermassive black holes.
In contrast, the new ORC is only six degrees above our galaxy’s plane. It appears to be incredibly close to the center of our Milky Way, but it could be even closer or much farther. The ORC has been given the nickname of Kýklos, which translates to “circle” in Greek.
Kýklos spans 80 arcseconds in the sky. The ring can only be seen at radio wavelengths. Even then, it is thin, faint and patchy, as it is only six arcseconds thick.
Jankovoy – stock.adobe.com – illustrative purposes only
It forms a near-perfect circle, and its radio spectrum is flat, so it doesn’t have any spectral lines, unlike other ORCs.
According to the European Space Agency’s Gaia mission, there are three galaxies that lie within Kýklos.
One galaxy is situated just three arcseconds from the ring’s center, but if Kýklos was produced by this galaxy, it doesn’t explain why the ORC has such a flat spectrum.
So, if Kýklos isn’t extragalactic, then it must be from the Milky Way. That means it originated from a star and is the remnant of a supernova.
However, supernova remnants generate X-rays as well, and no X-rays have been detected from Kýklos.
Possibly, Kýklos is a planetary nebula, a giant cloud of gas and dust thrown out by a dying star. Usually, a planetary nebula grows to roughly three light-years wide before scattering.
If Kýklos is a planetary nebula, it must be abnormally large or very near us. But planetary nebulas emit hydrogen-alpha light, which has not been detected.
The ring may have been produced by a massive and unstable Wolf-Rayet star. Its sheer size can generate a strong wind of radiation that blows deep into space.
No Wolf-Rayet star is present within Kýklos, but this makes sense because its powerful radiation wind likely destroyed the surrounding nebula. The flat spectrum also supports the Wolf-Rayet idea since the trait is typical of this type of star.
Moving forward, the astronomers will use the James Webb Space Telescope to try to solve the mystery of Kýklos.
A preprint version of the study is available on arXiv.
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