Sep 10, 2026

Chandra Found 84 Hypersoft X-ray Sources

Back to blog

The Chandra X-ray Observatory archive has just revealed a population that was visible, but only in the right band. On September 9, 2026, NASA announced that astronomers had identified 84 hypersoft X-ray sources across six galaxies, a new class of objects that emits very low-energy X-rays and intense levels of ultraviolet radiation.

The NASA/Chandra release says the sources were found in public Chandra data, including M101, the Pinwheel Galaxy, and M31, Andromeda. The study was published in Nature Astronomy the same day and argues that these objects may help explain two old questions: which systems precede some Type Ia supernovae, and which sources ionize gas between stars in certain galaxies.

Annotated M101 image with seven hypersoft X-ray sources marked
M101 with seven hypersoft sources marked. X-ray: NASA/CXC/Univ. of Alabama/M. Muhibullah et al.; optical: NASA/ESA/STScI; processing: NASA/CXC/SAO/N. Wolk

The clue hidden in the archive

The team searched for objects that appeared in the lowest-energy X-ray images and vanished in higher-energy images. That signature sounds straightforward, but it was exactly the blind spot: low-energy X-rays are hard to detect, and extreme ultraviolet radiation is readily absorbed by hydrogen and helium in interstellar space.

According to the official Chandra Photo Album, the M101 image combines Chandra X-ray data, shown in purple, with Hubble optical observations in red, green, and blue. The galaxy is roughly 21 million light-years away, and the composite spans a region about 86,000 light-years across.

Composite image of M101 with Chandra X-ray data and Hubble optical data
The unlabeled composite shows M101 in optical and X-ray light, where purple points reveal energetic sources. Image: NASA/CXC/Univ. of Alabama/M. Muhibullah et al.; NASA/ESA/STScI

What makes these objects strange is the combination: little emission above 0.3 keV, but enormous luminosity once the energy likely emerging in extreme ultraviolet is considered. The researchers suggest they may be binary systems, with a white dwarf, neutron star, or black hole pulling material from a companion star. Systems like that were already known; the novelty is how these shine at the hypersoft end of the spectrum.

What changes for you

For anyone who follows science from the outside, the importance is both methodological and practical. No new telescope had to be launched to find the clue; researchers had to return to existing data with a different question. That is a reminder that public scientific archives can keep producing discoveries years after the original observations.

There is also a direct link to cosmology. Type Ia supernovae are used as markers for measuring cosmic distances and were essential to the discovery that the Universe's expansion is accelerating. If some hypersoft sources are systems that precede those explosions, astronomers gain a better way to study what happens before the final flash, not only after it.

The other consequence is galactic. Intense ultraviolet radiation can strip electrons from gas between stars, changing how that gas cools, glows, and participates in forming new stars. If these sources are common, they may be a missing piece in models of galaxy evolution.

Chandra X-ray data for M101 used in the hypersoft-source discovery
The X-ray view isolates the signals that made it possible to search for objects almost invisible at other wavelengths. Image: NASA/CXC/Univ. of Alabama/M. Muhibullah et al.

The next step is to confirm what these objects are and how many more exist beyond the six galaxies studied. For now, the strong news is this: an entire class of cosmic sources may have been missed because it shone in the hardest place to observe. Chandra did not only find new points in an image; it found a new reason to reread the old sky.

Comments (70)

Sign in to comment. Register