Astronomers have found something hiding in nearby galaxies that they did not realize was there.
Using NASA's Chandra X-ray Observatory, researchers identified 84 mysterious cosmic sources with an unusual combination of extremely low-energy X-rays and intense ultraviolet radiation.
The objects behave differently enough from previously known populations that researchers have proposed a new class for them: hypersoft X-ray sources, or HSSs.
M101, the Pinwheel Galaxy, where seven of the newly identified hypersoft X-ray sources were found. Image credit: NASA/CXC/University of Alabama/M. Muhibullah et al.; NASA/ESA/STScI.
What Exactly Did Scientists Discover?
The discovery came from researchers examining observations stored in the Chandra X-ray Observatory archive.
Instead of looking for the brightest conventional X-ray sources, the team focused on objects appearing at the lowest X-ray energies accessible to Chandra.
They found something unusual.
The objects appeared in very low-energy X-ray observations but effectively disappeared when researchers looked at higher X-ray energies.
That extreme behavior is why the researchers named them hypersoft X-ray sources.
The team ultimately identified 84 of these sources across six nearby galaxies.
Where Are the 84 Objects?
The objects were not confined to a single unusual galaxy.
Researchers searched six galaxies and found hypersoft X-ray sources in all of them.
Two are famous spiral galaxies: M31 — better known as the Andromeda Galaxy — and M101, the Pinwheel Galaxy.
The other four are elliptical galaxies.
The sources also appeared in very different environments, including areas where stars are actively forming and regions dominated by much older stellar populations.
A surprisingly large population was identified.
The sources were found across multiple galactic environments.
Researchers call them hypersoft X-ray sources.
Seven of the newly identified objects are located in M101. An annotated Chandra image highlights their positions.
Why Are These Objects So Strange?
X-rays come in different energies.
Many familiar cosmic X-ray sources produce substantial radiation at higher X-ray energies.
These objects are different.
They emit almost exclusively at the softest X-ray energies accessible to Chandra, with little or no detectable emission at higher energies.
That suggests a significant amount of their radiation may actually be emerging in the extreme ultraviolet region of the electromagnetic spectrum.
The Mystery
- They are extremely soft X-ray sources.
- They appear to produce intense energetic ultraviolet radiation.
- They can be extraordinarily luminous.
- They exist in both young and old stellar environments.
- Astronomers still do not know exactly what objects are producing the radiation.
How Powerful Are They?
Their faint appearance in conventional X-ray observations should not be confused with a lack of power.
According to the Chandra research team, some hypersoft X-ray sources may radiate hundreds of thousands to millions of times more energy than the Sun.
Their luminosities can rival ultraluminous X-ray sources, among the brightest X-ray-emitting objects found away from the centers of galaxies.
In other words, these objects may have been difficult to detect not because they are insignificant, but because much of their energy appears in a part of the spectrum that is exceptionally difficult for astronomers to observe.
So What Are They?
That is the biggest unanswered question.
Researchers do not yet have a definitive identification.
The leading explanation is that many could be binary systems — two objects gravitationally bound together — where a compact object is pulling material away from a companion star.
| Possible Object | What Could Be Happening? |
|---|---|
| Black Hole | A black hole may be pulling matter from a companion star, heating the material before it falls inward. |
| Neutron Star | A dense neutron star may be accreting material from a stellar companion. |
| White Dwarf | A white dwarf may be collecting matter from another star, potentially creating conditions relevant to Type Ia supernovae. |
One possible explanation is a compact object — such as a black hole, neutron star or white dwarf — pulling material from a companion star.
Why Didn't We See Them Before?
This is one of the most fascinating parts of the discovery.
The universe has not suddenly created these objects. They may have been present in astronomical data for years.
Astronomers simply had difficulty seeing them.
Problem 1: Their X-rays Are Extremely Soft
The lowest-energy X-rays are difficult for X-ray telescopes to detect and can require long observations.
Problem 2: Ultraviolet Light Gets Absorbed
Hydrogen and helium gas between stars readily absorbs energetic ultraviolet radiation.
That creates what researchers describe as an extremely difficult barrier to seeing these objects directly at the wavelengths where much of their radiation may emerge.
Problem 3: Their Brightness Can Change
Researchers also note that large apparent variations in brightness may have contributed to the population remaining unnoticed.
Cosmic Mystery No. 1: Type Ia Supernovae
The discovery could become particularly important for understanding Type Ia supernovae.
These stellar explosions are extremely important in astronomy because their brightness allows scientists to use them as cosmic distance indicators.
Type Ia supernovae played a key role in the discovery that the expansion of the universe is accelerating.
Yet astronomers still have important unanswered questions about exactly which stellar systems explode and what triggers those explosions.
One possibility is that some white dwarfs pulling matter from companion stars eventually reach conditions that produce a Type Ia supernova.
Could Scientists One Day See a Supernova Before It Happens?
That possibility is one of the most exciting implications of the research — but it should not be overstated.
The new study does not mean scientists can now predict exactly when and where a Type Ia supernova will occur.
Instead, these sources may provide new candidates for studying the systems that can eventually lead to such explosions.
Understanding those systems before an explosion would give astronomers information they cannot obtain by studying only the aftermath.
Cosmic Mystery No. 2: What Is Ionizing Gas in Galaxies?
There is another puzzle.
Gas between stars can become ionized — meaning electrons are stripped away from atoms.
Scientists know hot, massive stars contribute energy capable of causing this process, but known stellar populations do not always appear to account for all of the required ionizing radiation.
The intense ultraviolet output potentially produced by hypersoft X-ray sources could help fill part of that missing-energy gap.
Why Ionization Matters
Ionization is not merely an obscure physics detail.
The state of gas inside galaxies can influence how that gas cools, how stars form and how galaxies evolve over enormous periods of time.
If astronomers have underestimated a large population of powerful ultraviolet sources, models of galactic environments may need to account for that additional energy.
Why M101 Is Important to This Discovery
M101 — the Pinwheel Galaxy — provides one of the most striking visual examples of the discovery.
It is a face-on spiral galaxy approximately 21 million light-years from Earth.
The composite released by the Chandra team combines X-ray observations from Chandra with optical data from the Hubble Space Telescope.
Seven of the newly discovered hypersoft X-ray sources are highlighted within M101.
The M101 composite combines Chandra X-ray observations with optical observations from the Hubble Space Telescope.
How Chandra Found Something Hidden in Old Data
There is another lesson in this discovery: new telescopes are not always required to make new discoveries.
Astronomical observatories collect enormous amounts of data, and those archives can remain scientifically valuable for decades.
Researchers searched publicly available Chandra observations for sources appearing at the observatory's lowest detectable X-ray energies.
By comparing those observations with higher-energy images, they could isolate objects with unusually soft spectra.
The approach exposed what had effectively been a blind spot.
Are These Objects Dangerous to Earth?
No evidence from the discovery suggests these objects pose any danger to Earth.
They were identified in other galaxies and are being studied because of what they may reveal about stellar evolution, supernovae and galactic environments.
Could There Be Thousands More?
Possibly.
The discovery of 84 sources in only six galaxies raises an obvious question: how many similar systems remain undetected elsewhere?
The research suggests astronomers may previously have missed large populations of binary systems producing energetic ultraviolet radiation.
Future observations and searches of additional galaxies could reveal whether hypersoft X-ray sources are relatively uncommon or widespread throughout the nearby universe.
What Scientists Need to Find Out Next
| Question | Why It Matters |
|---|---|
| What are the objects? | Scientists need to determine whether they involve black holes, neutron stars, white dwarfs or several different populations. |
| How common are they? | More galaxies need to be searched to estimate the true population. |
| How much UV do they produce? | This could determine their role in ionizing galactic gas. |
| Are some supernova progenitors? | This could help scientists understand Type Ia supernova explosions. |
| Why does their brightness change? | Variability could reveal the physical process powering the systems. |
Watch: A Tour of the Mysterious X-Ray Objects
Chandra's official release includes an animation and video tour explaining the newly discovered hypersoft X-ray sources.
Why This Discovery Is Bigger Than 84 Strange Dots
At first glance, 84 faint sources in distant galaxies might seem like a niche astronomical discovery.
The potential significance is much larger.
If these objects represent a previously overlooked population of energetic binary systems, they could change how scientists understand the energy environment inside galaxies.
If some are connected to Type Ia supernova progenitors, they could provide clues about stellar explosions that have been central to measuring the universe.
And if their ultraviolet radiation contributes significantly to ionizing gas, they could help explain another long-standing astrophysical puzzle.
Frequently Asked Questions
What did NASA's Chandra discover?
Researchers using Chandra data identified 84 unusual sources that emit extremely low-energy X-rays and appear to produce intense ultraviolet radiation.
What are hypersoft X-ray sources?
They are a newly identified class of cosmic sources that appear strongly at very low X-ray energies while producing little or no detectable higher-energy X-ray emission.
How many were discovered?
The researchers identified 84 hypersoft X-ray sources across six galaxies.
Where were they found?
They were found in six galaxies, including M31 — the Andromeda Galaxy — and M101, the Pinwheel Galaxy, along with four elliptical galaxies.
What could these objects be?
The leading possibilities involve black holes, neutron stars or white dwarfs pulling material from companion stars.
Are they dangerous?
There is no indication that the objects pose a danger to Earth. They are distant astrophysical systems being studied for their unusual radiation.
Why are scientists excited?
The objects may help researchers investigate the origins of Type Ia supernovae and understand sources of ionizing radiation inside galaxies.
Final Takeaway
The universe may have been hiding an entire population of powerful objects in plain sight.
By searching archival Chandra observations at extremely low X-ray energies, astronomers identified 84 sources with characteristics unlike previously recognized populations.
Scientists still do not know exactly what they are.
That uncertainty is precisely what makes the discovery so interesting.
They may involve black holes, neutron stars or white dwarfs. Some may potentially be connected to the systems that eventually produce Type Ia supernovae. Their intense ultraviolet radiation may also help explain how gas inside galaxies becomes ionized.
And after finding 84 of them in just six galaxies, perhaps the biggest question is now this:
How many more are still hiding across the universe?
- NASA Science — NASA's Chandra Unveils Mysterious X-Ray Objects, September 9, 2026.
- Chandra X-ray Center — M101 Photo Album and scientific release, September 9, 2026.
- Chandra Blog — A Hidden Population of Cosmic Beacons: Discovering Hypersoft X-ray Sources with Chandra.
- Nature Astronomy — Research paper describing the hypersoft X-ray source population.
Last updated: September 10, 2026.
