Images Show Entire "Universe" of Circular Structure That Can Only Be Seen as Radio Signals

The vast realm probed by radio astronomers is one invisible to the naked eye, and even most kinds of telescopes. 

Now, thanks to the latest advances in radio observatories, scientists are uncovering an entire "low surface brightness universe" teeming with circular curiosities, according to a team of researchers from Australia — including an entirely new class of cosmic object.

"It's comprised of radio sources so faint they have never been seen before, each with their own unique physical properties," writes Miroslav Filipovic, an astronomer at Western Sydney University, and his colleagues in an essay for The Conversation. "As we study the sky with telescopes that record radio signals rather than light, we end up seeing a lot of circles."

Allowing astronomers to delve into this uncharted realm include the Australian Square Kilometer Array Pathfinder (ASKAP), which is made up of 36 powerful antennas, and the South African MeerKAT radio telescope, comprising 64 antennas. Both are continuously involved in performing surveys of the night sky, but ASKAP in particular is leading one called the Evolutionary Map of the Universe (EMU) launched in 2022, which seeks to account for every radio source imaginable in the Southern sky.

In their essay, Filopovic and his colleagues document some of the most interesting objects this new generation of radio telescopes have found so far. Two of them are stellar oddities known as a Wolf-Rayet star. Dubbed Kýklos and WR16, these are massive celestial bodies, perhaps 25 times heavier than the Sun, near the end of their relatively brief lifespans. At this moribund stage, Wolf-Rayets rapidly shed mass, forming extremely luminous shells that, at their source, outshine our Sun by millions of times. That light is extremely faint by the time it reaches our planet, however, and since they only stick around for a few million years, spotting them is rare.

"In these objects, a previous outflow of material has cleared the space around the star, allowing the current outburst to expand symmetrically in all directions," wrote the astronomers. "This sphere of stellar detritus shows itself as a circle."

Radio imagery has also revealed a number of supernova remnants, or the sphere of gases and other material left behind after a massive star burns through its fuel, collapses under its own gravity, and epically explodes.

"The supernova remnant will be deformed by its environment over time. If one side of the explosion slams into an interstellar cloud, we'll see a squashed shape," explained Filipovic and company. "So, a near-perfect circle in a messy universe is a special find."

Lo and behold, ASKAP managed to spot one: a remnant named Teleios. And it's so perfect that nothing like it has ever been seen, according to the astronomers. "This presents us with an opportunity to make inferences about the initial supernova explosion, providing rare insight into one of the most energetic events in the universe," the scientists wrote.

Most mysterious of all is the latest instance (viewable here, on the right) of a new class of cosmic objects called Odd Radio Circles (ORCs), which, as the name suggests, are a phenomenon exclusively visible to the wavelength. ORCs are unfathomably large — large enough that they often imprison entire galaxies at their centers, with some being ten times as wide as the Milky Way.

Tantalizingly, this is just the beginning of our exploration of the "low-surface brightness universe," according to Filopovic, because the ASKAP and MeerKAT are just the prelude to the mother of all telescopes: the Square Kilometer Array, which, once completed, will be the biggest radio observatory in history.

More on space: James Webb Spots Mysterious Object Crossing Space Between Stars