Astronomers Uncover Previously Overlooked 'Hypersoft' X-Ray Sources

• Researchers identified 84 previously unrecognized celestial objects classified as Hypersoft X-ray Sources (HSSs) using archived data from NASA’s Chandra X-Ray Observatory.
• HSSs are characterized by high-energy emissions concentrated between 150 and 300 eV, often masking as extreme ultraviolet (EUV) emitters that are typically difficult to detect.

Challenges in Detection

• Standard data analysis often filters out energies below 300 eV to minimize background noise, which effectively hides these sources.
• Sensitivity degradation in Chandra’s ACIS camera, caused by outgassing coating the optical filters, further limited the detection of low-energy X-rays.
• The team successfully isolated these sources by analyzing specific datasets collected prior to 2017, when the telescope’s sensitivity was significantly higher.

Power and Potential Origins

• HSSs are incredibly luminous, with energy outputs ranging from tens to hundreds of thousands of times greater than the Sun’s total output.
• Proposed origins include:
  • Cooling white dwarfs in the aftermath of a nova.
  • White dwarfs accreting material from companion stars with expanded photospheres.
  • Black holes of stellar or intermediate mass featuring cooler accretion disks.

Implications for Cosmic Mysteries

• Type Ia Supernovae Progenitors: The discovered population may solve the long-standing mystery regarding the identity of stars that explode into standard-candle Type Ia supernovae.
• Interstellar Helium Ionization: HSSs could provide the missing energy required to explain the observed levels of helium ionization in the interstellar medium, which existing models struggle to account for.