Astronomers using the Australian Square Kilometre Array Pathfinder (ASKAP) have spotted a mysterious circular ring between the Milky Way’s plane and the Large Magellanic Cloud, a satellite of our Galaxy. Named J0624-6948, the object is most likely a remnant of a Type Ia supernova that exploded in the outskirts of the Large Magellanic Cloud and expanded into an intergalactic environment.
J0624-6948 was first detected with CSIRO’s Australian Square Kilometre Array Pathfinder (ASKAP), one of several new generation radio telescopes that are revealing new features of the Universe.
“These new radio telescopes can pick up a range of spherical objects, and due to the combined effects of high-sensitivity, good spatial sampling, and wide area coverage, they are enriching our understanding of the Universe,” said Professor Miroslav Filipovic, an astronomer at Western Sydney University.
“The discovery was exciting and raised many unanswered questions,” he added.
“When we originally discovered this almost perfectly circular radio object we thought it was yet another Odd Radio Circle (ORC) but after our additional observations, it became clear that this object is much more likely to be something else.”
The J0624-6948 ring had significant differences to the five other known ORCs — a flatter radio spectral index, lack of a prominent central galaxy as a possible host, and larger apparent size — that all suggested it may be a different type of object.
“The most plausible explanation is that the object is an intergalactic supernova remnant due to an exploded star that resided in the Large Magellanic Cloud outskirts that had undergone a single-degenerate type Ia supernova which involves the explosion of two stars orbiting each other,” Professor Filipovic said.
“However, we considered other scenarios such as that this object might represent a remnant of the super-flare activity from a nearby Milky Way star — at only 190 light-years away from Sun — that happened only a few centuries ago, or the premise that it may in fact be a much larger ORC.”
“What we’ve potentially then discovered is a unique remnant of supernova that has expanded into a rarefied, intergalactic environment — an environment that we didn’t expect to find in such an object.”
“Our estimates point to the age of about 2,200 to 7,100 years old.”
The discovery is reported in a paper in the Monthly Notices of the Royal Astronomical Society.
Miroslav D. Filipović et al. 2022. Mysterious Odd Radio Circle near the Large Magellanic Cloud — an intergalactic supernova remnant? MNRAS 512 (1): 265-284; doi: 10.1093/mnras/stac210
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