Published: 6 November 2026
A blind spot in the archive
Researchers searched public Chandra observations for sources visible at the lowest X-ray energies but absent at higher energies. They found 84 examples in six galaxies, including the spirals M31 and M101 and four elliptical galaxies.
Why hypersoft is unusual
The sources emit far more low-energy X-rays than high-energy ones and appear to produce intense ultraviolet radiation. That combination does not match any familiar population cleanly, which is why the researchers describe them as a possible new class rather than a solved category.
Three compact suspects
The leading explanation is a binary system in which a black hole, neutron star or white dwarf pulls material from a companion. Infalling gas heats and radiates before reaching the compact object. The spectrum reveals the energetic process, but it does not yet identify which compact object dominates the population.
Why astronomers missed them
Soft X-rays are difficult for telescopes to detect, while energetic ultraviolet light is readily absorbed by hydrogen and helium between the stars. Searching the archive with a deliberately low-energy filter exposed sources that had been hidden by both instrumental sensitivity and interstellar absorption.
Two possible cosmic consequences
Some accreting white-dwarf systems might be precursors of Type Ia supernovae, though that connection remains a hypothesis. The strong ultraviolet radiation could also help ionize gas between stars and influence star formation. Both possibilities require follow-up observations.
How to identify the engines
Astronomers can track variability, obtain ultraviolet spectra, search for companion stars and compare source locations with stellar populations. A mix of black holes, neutron stars and white dwarfs may ultimately explain the class better than a single answer.
Discussion question
When several compact objects can produce similar radiation, what observation would most decisively distinguish a black hole from a neutron star or white dwarf?
Sources and further reading
NASA Science — NASA's Chandra Unveils Mysterious X-Ray Objects ↗Share your answer
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