Astronomers have captured close-up images of a rare and mysterious space object, prompting renewed efforts to discover its origin. Odd Radio Rings (ORCs) are giant rings of radio waves. Only five have been sighted, and never in such spectacular detail.
The image of ORC J2103-6200 (also known as ORC1), taken by the high-resolution MeerKAT radio telescope in South Africa, has provided researchers with unprecedented information about these rare phenomena.Details are reported in a preprint, published this week on arXiv, and will be published on Monthly Notices of the Royal Astronomical Society.
“This discovery will start a new scientific study among astronomers,” said Alice Passetto, a radio astronomer at the National Autonomous University of Mexico in Mexico City.
New MeerKAT radio data show that ORC’s large outer ring may be over a million light-years across, ten times the diameter of the Milky Way, with a series of smaller rings inside. “It really reminds me of Faberge eggs or soap bubbles,” said Bärbel Koribalski, a radio astronomer at the Commonwealth Scientific and Industrial Research Organisation in Australia.
The first three ORCs, including ORC1, were discovered in 2019 using the Australian Square Kilometer Array Pathfinder (ASKAP) telescope. The fourth was found in 2013 in archival data from India’s Giant Meter-Wave Radio Telescope, and the fifth was last year’s data found by Koribalski in the updated ASKAP. Most orcs have a galaxy at their center, which astronomers think may have been involved in their creation. Equally confusing to scientists, ORCs are only found in radio wavelengths and not detected by optical or X-ray telescopes.
The researchers propose three theories to explain the origin of ORC. The first is that they are created by shock waves from the center of the Milky Way, similar to what happens when two supermassive black holes merge.
A second theory is that they are the result of active galactic nuclei activity, where radio jets eject particles to form the ORC’s shape. A third theory holds that ORCs are shells created by starbursts at the centers of galaxies. “Like detectives, we’re gathering more and more clues about what this object might be,” Corybarski said.
Due to its large field of view, most ORCs detected to date have been discovered using ASKAP. Whereas radio telescopes are usually able to observe an area the size of the moon, ASKAP can scan an area 100 times larger. Once ASKAP discovered ORC1, it used MeerKAT to examine it in more detail, as its higher resolution provides a sharper radio image.
“The ORC project is a great example of a user’s clever use of MeerKAT to its full advantage: ASKAP can observe large swaths of the sky and can discover relatively rare object types; MeerKAT can then follow up to study them in more detail,” Fernando Camillo, chief scientist at the South African Radio Astronomy Observatory in Cape Town, said in a press release. The observatory builds and operates MeerKAT.
Other high-resolution radio telescopes around the world may soon be pointing at these objects, especially after the next generation of these instruments comes online in the next few years, Korybalski said. These include the Square Kilometre Array, which will have thousands of antennas at two sites in Australia and South Africa, and the Next Generation Very Large Array in the US.
“There is no doubt that radio astronomers will be fascinated by this new type of object,” Passetto said.
This article is reproduced with permission, first published March 25, 2022.