Astronomers believe that they have finally figured out the origin of the huge “cosmic smoke rings”
The discovery of so-called “strange radio circles” a few years ago led astronomers to search for an explanation for these huge radio-emitting regions that extend so far that entire galaxies are at their centers. Scientists from the University of California in San Diego believe they have found the answer: the galactic winds from exploding stars in galaxies where the so-called “explosive star formation” of galaxies is to blame. They reported their findings in a new article published in the journal Nature.
“These galaxies are very interesting,” says Alison Coyle of the University of California, San Diego. “They arise when two large galaxies collide. As a result of the merger, all the gas is found in a very small area, which causes an intense burst of star formation. Massive stars burn up quickly, and when they die, they throw out their gas in the form of outward-directed winds.”
As previously reported, the discovery was made within the framework of the “Evolutionary Map of the Universe” (EMU) project, which aims to census radio sources in the sky. Several years ago, Ray Norris, an astronomer at the University of Western Sydney and CSIRO in Australia, predicted that the EMU project would make unexpected discoveries. He called them “WTF”. Anna Kapinska, an astronomer at the National Radio Astronomy Observatory (NRAO), was looking through radio astronomy data collected by the CSIRO Australian Square Kilometer Array Pathfinder (ASKAP) telescope when she noticed several strange shapes that didn’t look like any known type of object. Following Norris’ nomenclature, she labeled them WTF candidates. One of them was an image of a ghostly circle of radio radiation “hanging in space like a cosmic smoke ring.”
Other members of the team soon discovered two more strange circular spots, which they dubbed “odd radio circles” (ORCs). A fourth ORC was discovered in archive data from India’s giant MetreWave Radio Telescope, and a fifth in fresh ASKAP data in 2021. There are several other objects that can be ORCs. Based on this, the team believes that up to 1,000 ORCs may exist.
At first, Norris et al assumed that these spots were just imaging artifacts, but data from other radio telescopes confirmed that they are a new class of astronomical objects. They are not visible in standard optical telescopes, nor in the infrared and X-ray ranges – only in the radio range. Astronomers assume that the radio emission is caused by electron clouds. But this does not explain why ORC is not detected in other wavebands. All ORCs confirmed to date have a galaxy at their center, suggesting that this may be an important factor in their formation. In addition, they are huge – their size is about a million light years across, which is larger than our Milky Way.
As for the causes of the explosions that led to the formation of the ORC, new data presented in 2022 ruled out all but three possibilities. The first is that the ORC is the result of a shock wave from the center of the galaxy, possibly from the merger of two supermassive black holes. Alternatively, they may be the result of radio jets ejecting particles from active galactic nuclei. Ultimately, ORCs may be envelopes caused by star-forming bursts (the “final shock”) that create a spherical shock wave as hot gas escapes from the galactic center.