Overview
- A Chandra team led by Mustafa Muhibullah reported in Nature Astronomy on Sept. 9, 2026 that reanalysis of archival data turned up 84 objects the authors call hypersoft X‑ray sources across two spiral galaxies (M31 and M101) and four ellipticals.
- These sources appear only in Chandra’s lowest X‑ray energy channels and are inferred to emit copious extreme‑UV and ultraviolet light because low‑energy X‑rays sit next to UV on the spectrum.
- Researchers propose the objects are compact accreting binaries—white dwarfs, neutron stars, or black holes drawing gas from companions—but the team says the exact mix and detailed physics remain unconfirmed.
- Because EUV and UV photons are readily absorbed by hydrogen and helium, the 84 detected systems likely represent a small visible fraction of a much larger hidden population inside galaxies.
- The finding, born from careful reprocessing of two decades of Chandra archival data, opens a path for targeted UV, X‑ray and follow‑up observations that could identify Type Ia supernova progenitors and clarify what powers ionized gas in galaxies.