Astronomers Identify New Class of ‘Hypersoft’ X-Ray Sources in Nearby Galaxies
Using Chandra data, researchers discovered 84 objects in six galaxies that emit unusually low-energy X-rays together with intense ultraviolet radiation, labeling them hypersoft X-ray sources.
Scientists analyzing the Chandra X-ray Observatory archive identified 84 previously unknown objects across six galaxies, dubbing them hypersoft X-ray sources because they emit predominantly low-energy X-rays while producing bright ultraviolet light. Led by Mustafa Muhibullah of the University of Alabama, the search covered two spiral galaxies—M31 (Andromeda) and M101 (Pinwheel)—and four ellipticals, finding the sources in both star-forming and older stellar regions.
Their distinctive signature—visible only in the softest X-ray images and absent at higher energies—suggests they are binary systems involving a compact object such as a black hole, neutron star or white dwarf pulling matter from a companion star. This accretion process heats material to emit the observed radiation. Co-authors Jimmy Irwin and Rosanne Di Stefano note that such systems may represent a hidden population of progenitors for Type Ia supernovae and could be responsible for the ultraviolet photons that ionize galactic gas, influencing star formation. The discovery was reported in Nature Astronomy and highlights the value of re-examining archival data.
Why it matters
It uncovers a hidden class of energetic binaries that may solve key puzzles about supernova origins and galactic gas ionization.
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