Astronomers have discovered a new celestial object, a compact radio beacon located in the galaxy NGS 4945, about 12 million light-years away. Its light is polarized at an almost impossible level that hints at a perfectly aligned magnetic field. The object has been nicknamed "Punctum"; it’s a signal so clean and precise that it stands out like a lighthouse beam cutting through fog.
In a groundbreaking new study, astronomers at Instituto de Estudios Astrofísicos at the Universidad Diego Portales in Chile first spotted the new celestial object using the Atacama Large Millimeter/submillimeter Array (ALMA), during Band 3 observations (92-104 GHz) of the starburst galaxy NGC 4945. At the time, researchers were observing the bright, active core of the galaxy when they came across something unexpected.
Instead of the familiar pulsing heartbeat of a typical pulsar, this source emitted a steady radio signal, unusually compact and highly polarized. A combination that doesn’t fit neatly into any known category of cosmic objects. The team dubbed it Punctum, Latin for “point,” because it stands out like a pinprick of impossible order against the galaxy’s chaos.
“None of these known types matches Punctum’s exact combination of properties,” said Dr. Elena Shablovinskaia, lead author of the discovery, in an email to New Atlas. “So, at this stage we are effectively searching ‘under the lamppost’ of known objects while keeping an open mind about something novel.”
Under normal circumstances, light scatters chaotically as it travels through space, with its electric and magnetic fields vibrating in random directions. Polarization happens when those vibrations align in a single direction, something that usually only occurs under very specific conditions, such as when light passes through a uniform magnetic field.
“About 50% linear polarization at ~100 GHz is extraordinary,” Dr. Shablovinskaia explained to New Atlas, “because, in most cosmic sources, the light we detect comes from many regions with different magnetic directions, and so the polarization averages out. Such a high fraction means the radiation we see comes from a volume where the magnetic field is remarkably uniform, and that effects which normally blur or rotate polarization are weak at these wavelengths.”
To put that extraordinary polarization into perspective, think of waves rolling across the ocean. Normally they scatter, break, or twist in different directions under the push and pull of rocks, reefs, and shifting winds. Punctum’s light, however, behaves like a never-ending set of waves hitting the shore, and never losing formation. In cosmic terms, that means the magnetic fields guiding the light are unusually straight. Where most fields twist chaotically and scramble the signal, Punctum’s fields are highly aligned.
And for a distant radio source, sustaining 50% ± 14% polarization isn’t just remarkable - it approaches the theoretical maximum expected for synchrotron emission in a perfectly uniform magnetic field (around 70%). It means Punctum’s environment is extraordinarily ordered. That level of structure points to either a highly stable magnetic field or an unusual emission mechanism, perhaps tied to extreme astrophysical engines like magnetars.
So far, no X-ray counterpart has been seen with NASA’s Chandra X-ray Observatory and no cm-radio source with the Australia Telescope Compact Array (ATCA), making Punctum effectively invisible at those wavelengths.
So, what could Punctum be?
One hypothesis is that it may be a young, energetic pulsar whose beam is unusually stable. But its lack of the characteristic heartbeat pulse challenges that idea. Another possibility is that it’s a magnetar – a rare type of neutron star with a magnetic field trillions of times stronger than Earth’s – caught in an unusual emission state.
“From known classes, the most plausible options are a young, highly magnetized supernova remnant or neutron-star system (for example, a magnetar) or an extreme phase of a massive magnetic star,” Shablovinskaia said. “In other words, we expect a star-related object with a strong, ordered field – neutron stars, young supernova remnants, and magnetic massive stars are the catalogue of obvious candidates.”
In other words, Punctum doesn’t behave like either of its better-known cousins, and that’s exactly what makes it so intriguing.
Whatever its true nature, Punctum’s polarization makes it far more than a simple curiosity. By studying how the light’s polarization changes as it passes through interstellar space, astronomers can map the otherwise invisible magnetic fields that thread the fabric of space.
“Even if Punctum is not an entirely new class, it already demonstrates something new: compact, highly polarized millimeter sources can exist in dusty, star-forming nuclei and be invisible at optical, X-ray, or radio wavelengths,” said Dr. Shablovinskaia.
“That matters because millimeter polarimetry gives us a direct look at magnetic fields deep inside starburst regions – and magnetic fields strongly influence how stars form, how gas is moved around, and how energy is released into the surrounding medium. If there is a hidden population of such objects, we may be missing an important piece of energetic activity in galactic centers; finding more would change how we think about magnetic energy and its role in the life of galaxies.”
If more objects like Punctum can be found, they could become signposts for a new kind of galactic cartography, revealing structures we are unable to see with optical telescopes. That potential hinges on a key unknown: is Punctum a one-of-a-kind, or the first of many?
Follow-up observations to help answer these questions are already underway.
“We need coordinated, multiwavelength follow-up,” Shablovinskaia explained. She points to high-resolution ALMA polarimetry, very long baseline interferometry, sensitive radio imaging, and even JWST infrared searches as critical next steps.
“Together,” she noted, “these observations will provide us with the size, spectrum, polarization behavior, and IR/radio counterparts – the diagnostics needed to determine whether Punctum is a magnetar, a young supernova remnant, a magnetic star, or something else.”
If future observations reveal variability, it could point toward a pulsar or rotating neutron star. But if it continues to remain steady, it may signal something even more unusual.
For now, Punctum sits as a bright question mark in the sky. Its clean, unwavering signal offers both a hopeful clue and a challenge to our understanding of how the universe’s magnetic skeleton is built. Just as a compass needle reveals Earth’s magnetic field, Punctum may be the first of many cosmic beacons pointing to new ways of mapping the invisible forces that shape galaxies.
The team's study is available as a preprint on arXiv ahead of publication in the journal Astronomy & Astrophysics.
