A fresh look at telescope data reveals 84 mysterious objects

Astronomers have identified 84 examples of what may be a new class of cosmic source, uncovering signals that had gone largely unnoticed in observations of six galaxies.

The researchers searched publicly available data from NASA’s Chandra X-ray Observatory, concentrating on its lowest-energy measurements. The objects appeared in low-energy X-ray images but disappeared at higher energies, earning them the name “hypersoft X-ray sources.” They were found in both star-forming regions and areas dominated by older stars.

Their true nature remains uncertain. The leading explanation is that they involve compact stellar remnants, such as black holes, neutron stars or white dwarfs, pulling material from companion stars. The group may also contain several different kinds of systems. Their unusual emissions indicate that they produce intense energetic ultraviolet radiation, much of which is absorbed by hydrogen and helium gas before it can escape a galaxy. That could mean many more remain hidden.

Published in Nature Astronomy, the findings may offer clues to two persistent questions. Some white dwarf systems could be precursors to Type Ia supernovae, which are important for measuring cosmic expansion. The ultraviolet radiation might also help explain how gas between stars becomes ionized, a process that can influence star formation and the evolution of galaxies.