Chandra Discovers New Class of Hypersoft X‑ray Sources in Six Galaxies

Using data from the Chandra X‑ray Observatory, astronomers identified 84 hypersoft X‑ray sources—objects that emit unusually low‑energy X‑rays but intense ultraviolet radiation—in six nearby galaxies, including the Andromeda and Pinwheel spirals. The sources were found by detecting emission in Chandra’s lowest‑energy band that disappears at higher energies, indicating a spectrum dominated by soft X‑rays. The team suggests these systems likely involve a white dwarf, neutron star, or black hole accreting material from a companion star, producing both low‑energy X‑rays and copious ultraviolet light. Because the ultraviolet photons can strip electrons from interstellar gas, these objects may help explain the ionization observed in some galaxies. Additionally, the systems could represent a previously unseen population of binary stars that evolve into Type Ia supernovae, the standard candles used to measure cosmic expansion.