Distant Star's X-Ray Mystery Solved by White Dwarf

The star γ Cas, located in the constellation Cassiopeia, has long puzzled astronomers with its unusually intense and hot X-ray emissions. New data from the XRISM space telescope's Resolve instrument has identified a white dwarf companion as the source of these emissions. This breakthrough not only explains the phenomenon but also confirms the existence of a predicted, yet previously unobserved, class of Be + white dwarf binary systems.

These Be-type stars are known for rapid rotation and ejecting material into space. For decades, scientists debated the origin of γ Cas's strong X-rays, considering possibilities like magnetic activity or a close companion. XRISM's high-precision data revealed that the plasma's velocity shifts followed the white dwarf's orbital motion, directly implicating it in the X-ray production. The spectral features suggest this white dwarf is magnetic.

The confirmation of this binary system challenges existing models, particularly regarding mass transfer efficiency and the prevalence of lower-mass Be stars. This research has significant implications for understanding binary evolution, crucial for fields like gravitational wave research. The findings were led by researchers at the University of Liège and published in Astronomy & Astrophysics.