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Science Independently confirmed2 publishers 3 min read Published Updated

Eighty-four hypersoft X-ray sources surfaced in Chandra channels astronomers had skipped

The 84 detections came out of public Chandra data on six galaxies with no new observing time, and the class is defined by a spectral shape that co-author Jimmy Irwin thinks may cover three different kinds of stellar remnant.

The Scientist · Science desk

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What happened

  • Researchers report 84 objects they call hypersoft X-ray sources across six galaxies, all of them extracted from observations already sitting in the publicly available Chandra archive.
  • The sources were picked out because they show up in images made at Chandra's lowest X-ray energies and then vanish from images of the same fields at higher energies.
  • The team, led by University of Alabama doctoral candidate Mustafa Muhibullah, worked through Chandra data collected between 1999 and 2017 and filtered out random artifacts and other junk.
  • The searched galaxies are two spirals, M31 and M101, plus four ellipticals, and sources turned up both in regions of active star formation and among older stellar populations.
  • NASA says accreting binaries of this general kind have been observed before, but not producing such bright ultraviolet radiation together with such low-energy X-rays, and the paper appears in Nature Astronomy.

Why it matters

  • What's now possible capability Opening this detection window cost analyst time and nothing else, which makes any archive with channels its original users treated as noise a candidate place to look for objects nobody was pointing at.
  • What doesn't add up contradiction NASA's "new class of objects" and Irwin's "representation of what kind of energy is coming out" are not the same claim, and which one you accept decides whether follow-up chases a single physical model or sorts a mixed bag.
  • What it limits constraint Since the interesting radiation cannot reach Earth from most such systems, the population can only be bounded by modelling, which caps how firmly these sources can be credited with ionizing interstellar gas.
  • What it sets up precedent A Type Ia progenitor hunt that has come up empty now has a candidate list to work from, so the burden moves to showing which of the 84 contain white dwarfs rather than to finding candidates at all.

The selection carries its own control. A detector artifact or a cosmic-ray hit has no reason to respect a spectrum, so a point source that is present in the softest band and gone from the harder image of the same field [4] is not easily written off as junk, and the combination it implies, very soft X-rays alongside bright ultraviolet, is not one that known accreting binaries have shown [14]. Eighteen years of Chandra pointings went into the search [17].

The denominator deserves a note. Eighty-four objects across six galaxies works out to about 14 apiece [16], but that average is fragile: the targets are not a matched set [5], and the exposures are whatever the archive happened to hold [2]. What is published is a count, not a rate.

Then there is the word "class". Rosanne Di Stefano's reading is that these must be stellar remnants, a black hole, neutron star or white dwarf, ripping material off a companion that emits X-rays as it falls [7]. Jimmy Irwin puts the looseness on the record: "They're probably a heterogeneous mix of different types of objects," and "a hypersoft source isn't necessarily a type of object but a representation of what kind of energy is coming out" [8]. All that is known about the members so far is roughly how bright and how hot they are [9]. That makes the finding a spectral category which may contain three unrelated kinds of stellar corpse, a weaker claim than NASA's description of objects behaving unlike any seen before [10], and a more interesting one, because a category defined by output rather than by mechanism is exactly what you get when a detection window opens before the physics does.

Both advertised payoffs sit on the far side of that ambiguity. Accreting white dwarfs are candidate Type Ia progenitors, and those progenitors have been sought for years without success [18]; the extreme ultraviolet from these sources might account for ionized gas in galaxies that have no active nucleus to do the ionizing [19]. Each requires sorting the 84 into physical types first.

The thing this doesn't tell you is how many there are. The hydrogen and helium between the stars absorbs the energetic ultraviolet that makes these sources interesting [11], so the ones detected are the ones sitting where the light escapes. Di Stefano says each source seen stands for many more in the same galaxy that cannot be, the tip of an iceberg [20]. An ionizing budget built on hypersoft sources therefore runs through a hidden-to-visible ratio that nobody has measured.

The part of this that travels beyond one paper is the least glamorous. According to Irwin, the very lowest-energy channels were passed over for years because they were thought unimportant [12], and a doctoral candidate and two colleagues reading them anyway [3] produced 84 detections without an hour of new telescope time [2].

What to watch

  • Optical or ultraviolet counterparts that pin individual sources to a white dwarf, a neutron star or a black hole.
  • Whether the same soft-band selection applied to more of the Chandra archive turns up sources in other galaxy types.
  • An independent reprocessing of the 1999 to 2017 data that recovers the same 84 objects after artifact filtering.

Clarity's read

What the record supports and how the coverage leans. The claims behind it follow.

Reality

Evidence64
Adoption
Not scored
Hype gap+30
Incentives45
Confidence62

Perspective Coverage

3 publishers
Builder
Builder 62%
Operator
Operator 33%
Investor
Investor 5%
Why these scores

Claim ledger

Ranked by verification strength, evidence, and original report placement.

  1. [1]

    The discovery is featured in a paper published Wednesday in Nature Astronomy.

    Reported SupportedView cited source
  2. [2]

    Researchers found a total of 84 "hypersoft X-ray sources" in the six galaxies they searched, using data openly available to the public in the Chandra archive.

    Reported SupportedView cited source
  3. [3]

    The study was led by Mustafa Muhibullah of the University of Alabama, a PhD candidate; co-authors include Alabama professor Jimmy Irwin and Rosanne Di Stefano, a lecturer at the Center for Astrophysics | Harvard & Smithsonian.

    Reported SupportedView cited source
  4. [4]

    The team spotted the sources by finding objects that appeared in Chandra 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.

    Reported SupportedView cited source
  5. [5]

    Two of the six galaxies are spirals, M31 (Andromeda) and M101 (the Pinwheel), while the other four are ellipticals.

    Reported SupportedView cited source
  6. [6]

    Hypersoft X-ray sources were found both in regions of active star formation and in areas where there are older stars.

    Reported SupportedView cited source
  7. [7]

    Di Stefano: "They must be compact objects that are the remnants of stars, either black holes, neutron stars or white dwarfs, that are ripping material from the companion. And as the material falls, it emits at x-ray wavelengths."

    Reported Supported Source: Rosanne Di Stefano, Center for Astrophysics | Harvard & SmithsonianView cited source
  8. [8]

    Irwin: "They're probably a heterogeneous mix of different types of objects" and "A hypersoft source isn't necessarily a type of object but a representation of what kind of energy is coming out."

    Reported Supported Source: Jimmy Irwin, University of AlabamaView cited source
  9. [9]

    What exactly these objects are is a mystery because all that is known about them is roughly how bright and how hot they are.

    Reported SupportedView cited source
  10. [10]

    NASA describes the result as the discovery of a new class of objects behaving unlike any scientists have seen before.

    Reported SupportedView cited source
  11. [11]

    The high-energy ultraviolet radiation is readily absorbed by helium and hydrogen gas filling the space between the stars, creating a nearly impenetrable barrier to look through.

    Reported SupportedView cited source
  12. [12]

    Irwin: scientists "didn't even know the objects were there" and "ignored the very, very lowest-energy channels because they thought they were unimportant."

    Reported Supported Source: Jimmy Irwin, University of AlabamaView cited source
  13. [13]

    Irwin: "If we had a telescope that was sensitive to EUV and we didn't have the fog, these sources would be booming bright in these galaxies, and they would not have been missed."

    Reported Supported Source: Jimmy IrwinView cited source
  14. [14]

    Binary systems of this kind have been seen before, but not with such bright ultraviolet radiation and low-energy X-rays.

    Reported SupportedView cited source
  15. [15]

    The three researchers scoured data collected by Chandra between 1999 and 2017 and painstakingly filtered out random artifacts and other junk.

    Reported SupportedView cited source
  16. [16]

    The 84 sources average about 14 per searched galaxy.

    Derived Supported
  17. [17]

    The archival data searched spans 18 years of Chandra observations.

    Derived Supported
  18. [18]

    Some white dwarf systems pulling material from companion stars may eventually explode as Type Ia supernovae, which are critical for measuring the expansion of the universe; astronomers have been looking for the stars that turn into Type Ia supernovae for many years, so far without success.

    Reported InsufficientView cited source
  19. [19]

    Active galactic nuclei are generally credited with helping ionize gas that later forms stars, but some galaxies lack these black holes and still have ionized gas, which hypersoft emitters could help explain.

    Reported InsufficientView cited source
  20. [20]

    Di Stefano: "The sources that we see, each one represents many additional sources within the galaxy that we cannot see because the light never makes it out of the host galaxy"; "We're seeing the tip of the iceberg."

    Reported Insufficient Source: Rosanne Di StefanoView cited source
  21. [21]

    The discovery suggests there may be large populations of binary systems with energetic ultraviolet radiation that have been undetected until now.

    Reported InsufficientView cited source
  22. [22]

    Stripping of electrons from gas between the stars can affect how quickly stars form and influence galaxy life cycles; hot, massive stars play a role but do not completely explain it.

    Reported InsufficientView cited source

Sources

2 independent publishers whose own reporting we read for this story.

  1. nasa.gov

    1 article · September 9, 2026

    NASA’s Chandra Unveils Mysterious X-Ray Objects
  2. phys.org

    1 article · September 9, 2026

    Chandra uncovers 'hypersoft X-ray sources' that may solve two astrophysical puzzles
  3. scientificamerican.com

    1 article · September 9, 2026

    Astronomers reveal a new type of celestial object that has been hiding in plain sight for decades

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