It hangs in the sky like a cosmic bubble, eerily round, barely glowing in the radio spectrum.
Among the wreckage of the Milky Way — where the violent deaths of stars usually leave chaos and crumpled shells — astronomers have found something unsettling: a nearly perfect circle. They call it Teleios, from the Greek for “perfect,” and in a universe shaped by turbulence and asymmetry, its symmetry is not just unusual. It’s uncanny.
“It’s one of the most circular remnants ever found in our galaxy,” wrote the astronomers led by Dr. Miroslav Filipović of Western Sydney University.
Supernova remnants simply don’t look like this. They’re messy. This one isn’t.
The discovery has raised a simple but confounding question: how does a star explode with such grace?
A supernova remnant with a mysterious origin
Teleios was spotted serendipitously during the Evolutionary Map of the Universe (EMU), a sweeping radio survey conducted by ASKAP, a radio telescope array located in Australia. The remnant, officially designated G305.4–2.2, appeared as a faint ring of radio emission just over two degrees below the Milky Way’s galactic plane.
To the naked eye, Teleios would be invisible. It glows only in the radio spectrum, with no detectable infrared, optical, or X-ray counterpart. “Interestingly, Teleios is not only almost perfectly symmetric, but it also has one of the lowest surface brightnesses discovered among Galactic SNRs,” the authors noted in their research paper.
And that’s just the start of the puzzle.
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Determining the distance to cosmic objects is notoriously tricky. Based on different models, Teleios could be relatively nearby at around 2.2 kiloparsecs (7,175 light-years), or more distant at 7.7 kiloparsecs (25,100 light-years). These two possibilities carry starkly different implications.
If closer, Teleios spans about 14 parsecs (46 light-years), and may be less than 1,000 years old. That would make it a cosmic adolescent. But if it’s farther away, the shell balloons to 48 parsecs (157 light-years) across — and the remnant would have to be at least 10,000 years old.
Either way, it’s still unusually spherical. Most supernova remnants are warped by uneven explosions or lumpy gas in the surrounding interstellar medium. Yet Teleios has kept its form. “Maintaining a perfectly symmetrical shape for a size greater than ~10 pc would require an unreasonably low magnetic field strength,” the team wrote.
Type Ia? Or something stranger?
So, what could cause such a symmetrical structure?
The researchers believe Teleios most likely formed from a Type Ia supernova — an explosion triggered when a white dwarf star, bloated by gas siphoned from a companion in a binary system, grows too massive and detonates. Type Ia supernovae are typically bright and clean, leaving little residue, and are known for their relative symmetry.
But this scenario presents a problem: it should produce detectable X-ray emission. Teleios shows none.
That’s where a more exotic idea comes in. Perhaps Teleios is the remnant of a Type Iax supernova, a close cousin of the standard Type Ia, but weaker and weirder. Type Iax events don’t completely obliterate the white dwarf. They can leave behind a kind of “zombie star,” smoldering quietly after the blast.
This fits the radio data — and the lack of X-rays — but only if Teleios is much closer, at just 3.3 parsecs (11 light-years) in diameter. That’s a tough case to make. Other observations, including hydrogen data from the HI4PI survey, suggest the remnant lies farther out.
And there’s more. One curious star sits near the remnant’s center, which might be the leftover white dwarf. But parallax data from Gaia shows the star is much closer than Teleios is likely to be. That makes it an unlikely candidate.
As the researchers put it: “All possible scenarios have their challenges . . . and new sensitive and high-resolution observations of this object are needed.”
A remnant suspended in silence
Part of what makes Teleios so perplexing is how ‘quiet’ it is.
Despite efforts using NASA’s Fermi gamma-ray space telescope and data from the H.E.S.S. observatory in Namibia, there’s only a faint whisper of gamma-ray emission from the region. There’s no pulsar, no glowing X-ray cloud, no heat signature in infrared. Just a radio shell, symmetrical and faint, alone in the dark.
The team suspects the low-key Teleios exploded in a rarefied pocket of interstellar gas, perhaps even inside a cavity carved out by earlier stellar winds. That would help preserve its shape and explain the low levels of emissions. “Expansion into an isotropic but rarefied environment could help explain Teleios’s remarkable circularity,” the study notes.
Similar remnants have been found, like the circumgalactic SNR J0624–6948. But even among those, Teleios stands out. Its circularity exceeds 95%, higher than any other remnants.
Why this matters
Supernova remnants are essential to galactic evolution. They scatter heavy elements into space, trigger star formation, and help sculpt the interstellar medium. Yet many remain undiscovered — scientists estimate the Milky Way hides as many as 2,000 remnants that current instruments have yet to detect.
ASKAP is helping change that. Teleios joins a growing list of “invisible” supernova remnants revealed through radio astronomy.
But it’s more than a curiosity. If Teleios is indeed the product of a Type Iax explosion, it would represent a rare opportunity to study this peculiar class of supernovae up close. And if it’s a typical Type Ia, then its symmetry — and lack of electromagnetic emissions — challenge existing models of how such explosions evolve.
In either case, it’s a reminder that the Milky Way still holds plenty of secrets.
The findings appeared in the journal arXiv.