Astronomers detect another mysterious ghostly circle in extragalactic space
The discovery of a giant ghostly circle in extragalactic space brings us closer to understanding these mysterious structures.
The so-called odd radio circle, named ORC J0102-2450, joins just a handful of previously discovered space blobs. Given the small sample size, the new discovery adds important statistical data that suggests these objects could somehow be linked to galaxies. The paper was accepted in Letters from MNRAS, and is available on the pre-print server arXiv.
Humanity has been looking and wondering about the sky for tens of thousands of years, but even so, space retains many secrets. Weird radio circles – ORCs – were only discovered last year, in 2019 observations collected by the Australian Square Kilometer Array Pathfinder (ASKAP), one of the most sensitive radio telescopes in the world.
As the name suggests, these are apparently giant circles of relatively faint light in radio wavelengths, appearing brighter at the edges, like bubbles. Although circular objects are relatively common in space, ORCs appear to correspond to no known phenomenon.
Follow-up observations with a different telescope array confirmed the presence of two of the original three ORCs, while a fourth was quickly found in data collected by another instrument. So we can be quite confident that this is not the result of an ASKAP problem or artifact, or a local phenomenon at the telescope (like the Murriyang microwave oven) or.
We don’t know how far the ORCs are, making their size difficult to assess, but finding more could give us more clues. This is where ORC J0102-2450 comes in.
ASKAP conducted a series of radio continuum observations between 2019 and December 2020. To find the ORC, a team led by astronomer Bärbel Koribalski of CSIRO and the University of Western Sydney in Australia combined eight of the continuum images radio, a process that reveals objects too faint to be seen in just one or two images.
From the combined data, a slight ring emerged. Comparison with observations from other surveys did not reveal any radiation in wavelengths other than radio, which may help rule out some emission sources.
Interestingly, however, almost in the center of ORC, the team found something: an elliptical galaxy radio, named DES J010224.33-245039.5.
Of course, that could be a coincidence – but two of the other four ORCs described last year also had an elliptical galaxy radio boom in the middle. The chance of finding a radio source randomly coinciding with the center of an ORC is one in two hundred, the researchers said – not to mention finding three of those things.
This suggests that the circles may have something to do with elliptical radio galaxies. We know that radio galaxies often have radio lobes, huge elliptical structures that emit only in radio wavelengths that swell on either side of the galactic nucleus. One possibility is that the ORCs are these lobes seen end-to-end, so that they appear circular.
ORCs could also, the researchers noted, be the product of a giant shock wave from the central galaxy, but it would take really giant, produced by something like the merger of two supermassive black holes.
If either of these scenarios is the case, the galaxy connection can help us determine the size of the ORC. In the case of ORC J0102-2450, we know the distance to DES J010224.33-245039.5. This distance gives us a rough estimate of the size of ORC J0102-2450 of about 980,000 light years. If this size is confirmed, it could help us learn more about radio lobes or blast waves.
The third possibility the researchers have considered is an interaction between a radio galaxy and the intergalactic medium, possibly involving DES J010224.33-245039.5, although it seems relatively unlikely to produce the observed ring, the team noted. .
Although the sample size is still extremely small and we can’t say anything for sure yet, the discovery of ORC J0102-2450 points to promising directions for future observations and analysis.
If we can find even more ORCs, they should be able to help astronomers determine their frequency and find more similarities between them that could further refine their potential training mechanisms.
Low-frequency radio observations and x-ray observations will be of particular interest, they noted.
“The discovery of other ORCs in the rapidly growing amount of wide-field radio continuum data from ASKAP and other telescopes will show whether the above scenarios have any merit, contributing to exciting times in astronomy,” said writes the team in their article.
The paper was accepted in Letters from MNRAS, and is available on arXiv.