The X-ray Trail of the Solar Wind express
The solar wind, a stream of charged particles from the Sun, slams into the tenuous gas that fills the space between the stars. The collision produces a faint X-ray glow. For astronomers, this is like fog in front of headlights: it obscures distant objects. The eROSITA telescope aboard the SRG space observatory scanned the entire sky four times, gathering data free from the interference of Earth's atmosphere. Scientists calculated the contribution of this glow and subtracted it from the overall picture.
The result is a map of the diffuse X-ray sky in the western part of the Galaxy — now without the extra background. But the real surprise is this: it turns out that this glow can be used to track how interstellar matter flows through the Solar System. Just as the haze from headlights reveals the direction of the wind on the road.
Original abstract
as written by the authors arXiv:2604.26003
Solar wind charged particles interact with diffuse gas within the heliosphere, producing soft X-rays. This solar wind charge exchange (SWCX) process produces foreground emission that complicates interpretation of X-ray observations. In this work, we analyze X-ray observations of the western Galactic hemisphere by the Extended Roentgen Survey with an Imaging Telescope Array (eROSITA) instrument on the Spectrum-Roentgen-Gamma (SRG) spacecraft. These data avoid contamination by Earth's geocorona and are derived from four surveys of the full sky, including during the minimum of the Sun's activity cycle. We determine the SWCX contribution and subtract it from the survey, providing a less contaminated view of the diffuse soft X-ray sky. We also demonstrate that X-rays can be used to map the flow of interstellar matter through the Solar System.
The glow from solar wind charge exchange was first noticed back in the 1990s, but only now has it been neatly subtracted from a full-sky survey.