Overview
- The University of Liège–led team reported the result Tuesday in Astronomy & Astrophysics after XRISM’s Resolve spectrometer tracked the X‑ray‑emitting gas across the system’s 203‑day orbit.
- High‑resolution spectra showed Doppler shifts in iron emission and fluorescence lines that matched the compact companion’s motion, linking the hard X‑rays to accretion onto the white dwarf rather than activity on the Be star.
- The measured line widths were only about 200 km/s, which rules out a non‑magnetic inner‑disk origin and points to a magnetic white dwarf that channels infalling gas to its poles.
- The work establishes γ Cas and its analogues as Be + white dwarf binaries, a group that appears to include roughly 10% of early‑type Be stars and favors higher‑mass Be stars than theory expected.
- Be stars are fast‑spinning, massive stars that shed gas into a surrounding disk, and this confirmation will drive updates to binary‑evolution models that feed into forecasts for how massive stars end their lives and create gravitational‑wave sources.