Last updated: 15.01.2024, 04:53 a.m.
By: Tanja Banner
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An "odd radio circle" (ORC) taken by the MeerKAT radio telescope (green object), the background is from the Dark Energy Survey. © J. English (U. Manitoba)/EMU/MeerKAT/DES(CTIO)
Strange radio circles in the universe, known as ORCs, have long occupied science. Now there seems to be an explanation.
San Diego – In 2019, they were discovered for the first time: mysterious rings in space that are not visible in either the optical or infrared range. They also don't emit X-rays – only radio waves. That's why they are called "odd radio circles" (in German "strange radio rings") and abbreviated ORCs. To date, few of these unusual structures have been discovered, and while there are some theories, an explanation for their existence is still lacking. But now the mystery of the strange circles in the universe may be solved. The study was published in the journal Nature.
A team of researchers led by Alison Coil of the University of California San Diego has found a possible explanation for the origin of the ORCs. The scientists focused on so-called "starburst" galaxies, i.e. galaxies in which an unusually high number of stars are formed. "These galaxies are really interesting," Coil said in a statement from her university. "They are formed when two large galaxies collide. By merging, all the gas is forced into a very small region, resulting in an intense burst of star formation."
ORCs are apparently formed by the galactic winds of dying stars
But that's not all, as Coil continues: massive stars would burn out quickly, and when they die, they would eject their gas as outflowing winds. According to the researcher, this process could lead to the strange radio circles: If enough stars explode in close proximity to each other at the same time, the explosion can push the gas out of the galaxy. The winds could reach speeds of up to 2000 kilometers per second – and create the OCRs.
However, Coil explains that a number of prerequisites are necessary for this to work: "For this to work, you need a massive outflow, which means that a lot of material is ejected very quickly. And the surrounding gas outside the galaxy must have a low density, otherwise the shock will stop. These are the two key factors."
Her research team found that the galaxies they studied would have these high mass outflow rates, Coil continues, adding, "They may be rare, but they do exist. I really believe this suggests that ORCs originate from some kind of outgoing galactic winds." (tab)
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