Determine the physical origin of the Galactic hot soft X-ray component

Determine the physical origin of the Milky Way’s hot soft X-ray component, including whether it is dominated by stellar coronal emission, diffuse plasma associated with Galactic outflows or the halo, or a hybrid combination of these sources.

Background

The paper distinguishes a warm-hot soft X-ray component with a characteristic temperature of approximately 0.2 keV from an additional hot, super-virial component with temperatures of roughly 0.5–1 keV. The hot component has been detected along multiple lines of sight, but its physical source is unresolved.

Two principal explanations are discussed: unresolved stellar emission, particularly from low-mass dM stars, and diffuse plasma produced by star-formation-driven outflows or distributed beyond the Galactic disk. The authors’ all-sky spectral and spatial analyses support a possible composite origin, but do not establish the relative contributions of stellar and diffuse emission.

References

The origin of the hot component therefore remains uncertain and may have a single dominant origin or may instead represent a hybrid component in which stellar emission and diffuse plasma both contribute.

— Probing the All-sky Distribution of Soft X-ray Emission Associated with the Milky Way  (2609.16688 - Ampuku et al., 15 Sep 2026) in Section 1, Introduction