The universe is not a chaotic free for all. Most of the stars are bound up in galaxies, which are separated by huge, almost unimaginable distances.
The space between the galaxies – the intergalactic space – is sparsely populated, but not completely empty; there you can also find some lone stars.
For the first time, astronomers believe they have found evidence of the death of one of these lone rogue stars. Not far from the large Magellanic cloud, a satellite galaxy orbiting the Milky Way, is a mysterious and remarkably neat circle that emits radio waves, has been discovered, hanging in space and called J0624-6948.
If it sounds familiar, there is a reason for it. Recently, astronomers have been amazed at several mysterious, radio-emitting space circles, called Odd Radio Circles or ORCs.
The similarity was not lost on the astronomer Miroslav Filipovic from the University of Western Sydney in Australia.
“When we originally discovered this almost perfectly circular radio object, we thought it was yet another ORC,” he says. “But after our further observations, it became clear that this object is much more likely to be something else.”
ORCs were first discovered using one of the world’s most powerful radio telescopes, the Australian Square Kilometer Array Pathfinder (ASKAP) in Australia. These objects appeared to be enormous and distant, with several defining characteristics, not least of which is a galaxy in the dead center.
Scientists now believe that the ORCs are the result of an energetic process in these central galaxies, although the exact nature of this process is unknown.
In fact, it is likely that ORCs are actually spheres. The reason they appear poor is because of perspective; around the edges there is a greater density of emission along our line of sight.
Still, there are a few important differences between J0624–6948 and ORCs. The lack of an obvious central galaxy in J0624–6948 is large, but not crucial in itself. The spectral index for radio emission is flatter than for ORCs, and the apparent magnitude of J0624-6948 is also different – larger than the other ORCs.
Filipovic and his team considered a number of possibilities that could result in an object similar to their observations. These included a much larger ORC, as well as a super-flare originating from a star near the galactic center, or jets from a distant active supermassive black hole.
In the end, one scenario stood out as the most consistent with the observed phenomenon.
The most plausible explanation is that the object is an intergalactic supernova remnant due to an exploded star located at the edge of the Great Magellanic Cloud, which had undergone a single-degenerate type Ia supernova, which involves the explosion of two stars orbiting each other, “Filipovic explains.
“What we potentially then discovered is a unique remnant of [a] supernova, which has expanded into an obsolete, intergalactic environment – an environment we did not expect to find in such an object. Our estimates point to an age of about 2,200 to 7,100 years old. “
Although supernova remnants do not tend to be so beautifully circular, it would not be without precedent. A handful of similar examples, such as the stunning eye-shaped object SN 1987A in the large Magellanic cloud, have been documented.
If scientists are right, J0624-6948 would be the first intergalactic supernova remnant ever identified – a bubble-like sphere of ejecta that extends outward. According to the team’s measurements, an attachment to the large Magellanic cloud would make J0624-6948 about 155 light-years across.
Follow-up observations can help resolve the uncertainty. In addition, several observations with instruments such as ASKAP and its South African counterpart MeerKAT could help identify more peculiar radio circles in the sky.
Finding more will give us a more complete picture of their range and diversity, giving us a better chance of finding out what they are.
“These new radio telescopes can pick up a variety of spherical objects,” says Filipovic. “Because of the combined effects of high sensitivity, good spatial sampling, and wide area coverage, they enrich our understanding of the universe.”
The research has been published in Monthly announcements from the Royal Astronomical Society.