They were hiding in plain sight for years. Now astronomers think these 84 cosmic enigmas could solve two of the biggest mysteries in physics.
Imagine discovering 84 powerful lamps in thick fog — not by seeing their light directly, but by noticing only the faintest glow escaping through the haze. That’s essentially what a team of astronomers just did with NASA’s Chandra X-ray Observatory. After digging through decades of archival data, they found 84 objects scattered across six nearby galaxies that emit unusually low-energy X-rays but produce intense levels of ultraviolet radiation — a combination never seen before.
The discovery, published in Nature Astronomy, has been described by researchers as “unlike anything seen before”. And the implications are enormous.
What Exactly Did They Find?
The objects are being called “hypersoft X-ray sources” — “soft” meaning their X-rays carry relatively little energy. But that’s where the familiarity ends. Most of their radiation likely emerges as extreme ultraviolet (EUV) light, which lies between ultraviolet light and X-rays. The problem? Interstellar gas absorbs EUV light before it can reach our telescopes. Chandra can only detect the faint, low-energy X-ray tail of that emission.
“We’ve never encountered a group of objects that act like this,” said Mustafa Muhibullah, a Ph.D. candidate at the University of Alabama who led the study. “Of course, the next step was to try to figure out what these things are”.
The 84 sources were found in six galaxies: two spiral galaxies — Andromeda (M31) and the Pinwheel Galaxy (M101) — and four elliptical galaxies. The team spotted between 7 and 21 sources in each galaxy.
How Did They Hide for So Long?
The objects were sitting unnoticed in Chandra’s archive because they’re incredibly difficult to detect. The team found them by looking for objects that appeared in images taken at the lowest X-ray energies but vanished in higher-energy images — meaning they give off far more low-energy X-rays than high-energy ones.
But how do we know these aren’t just detector errors? The first clue was repetition: many appeared at exactly the same positions in observations made at different times. A random error wouldn’t keep returning to the same place. Some were also independently detected by the XMM-Newton telescope. And their locations offered a second clue — in M101, many followed the galaxy’s spiral arms, while others appeared among older stars in elliptical galaxies. Fewer than 3 percent are expected to be unrelated objects.
“What surprised us most is that, despite being so difficult to detect, they can be extremely luminous,” Muhibullah told ScienceAlert. Some of these objects may release hundreds of thousands to millions of times more energy than the Sun.
The Two Cosmic Mysteries They Could Solve
This is where things get genuinely exciting. Researchers believe these objects could help resolve not one, but two long-standing puzzles in astrophysics.
Mystery #1: What triggers Type Ia supernovae?
When a star like the Sun dies, it can leave behind a white dwarf — an Earth-sized core packed with enormous density. If the white dwarf has a companion star, it can pull gas from it. That stolen gas collects on the white dwarf, making it hotter and heavier. In some cases, the white dwarf eventually destroys itself in a colossal explosion called a Type Ia supernova.
These explosions are critical to astronomy. They’re so consistently bright that they can be used to measure cosmic distances — and they played a key role in discovering that the expansion of the universe is accelerating. But astronomers have never been able to identify which star systems are about to explode.
“If we could find a way to spot these Type Ia supernova explosions before they go off, that would be really important,” said co-author Jimmy Irwin. “Right now, we study them after they’ve exploded, and astronomers have struggled to understand what is actually ignited”.
The newly discovered hypersoft X-ray sources may be the missing link — the progenitors of these explosions, caught in the act of feeding.
Mystery #2: What strips electrons from interstellar gas?
The second puzzle is what causes gas between stars in certain galaxies to lose its electrons — a process called ionization. This matters because ionization affects how quickly stars form and shapes the life cycles of galaxies. Hot, massive stars contribute to this process, but they don’t fully explain it. The intense ultraviolet radiation from these hypersoft X-ray sources could be the missing factor.
What Are They, Really?
The honest answer is: we don’t know yet. The team thinks the objects most likely involve a black hole, neutron star, or white dwarf pulling material from a companion star. The material is heated to produce X-rays before falling onto the compact object. Such binary systems have been seen before — but never with such bright ultraviolet radiation and low-energy X-rays.
“Hypersoft” may not describe one kind of object at all. It may describe the unusual light reaching the telescope — and several different cosmic systems could be producing it.
And 84 may only be the beginning. Chandra collects very little light at these energies, and contamination on its detectors has reduced its ability to do so. The team may have found only the brightest members of a much larger, hidden population.
What Happens Next
Researchers are already planning further observations to determine the precise nature of these objects and examine their influence on shaping galaxies. The discovery suggests there may be large populations of binary systems with energetic ultraviolet radiation that have been undetected until now.
“These clandestine X-ray sources are actually among the most energetic objects in galaxies,” Muhibullah said, “and they could be solving two cosmic mysteries at once”.
The universe, it turns out, is full of things we’ve been looking at without seeing. These 84 objects were always there, hiding in the archives, waiting for someone to notice the faint glow escaping through the fog. Now that we’ve found them, the question is what else is still hiding in the dark.
