🌟 The mystery of emissions from the star Gamma-Cassiopeiae solved

For over a century, the star named Gamma-Cassiopeiae (or "Gamma-Cas") has puzzled astronomers. Visible to the naked eye in the northern hemisphere, this massive star emits powerful light and X-rays that have long resisted any explanation.

Located about 550 light-years away, Gamma-Cassiopeiae far surpasses our Sun in size and luminosity. As early as the 19th century, its atypical hydrogen signature was noted, followed in the 1970s by the detection of intense X-ray emissions.


For decades, scientists have explored various leads to elucidate these emissions. Some hypotheses involved magnetic interactions, while others postulated the existence of a hidden companion. The advent of X-ray space telescopes, such as XMM-Newton and Chandra, made it possible to identify other similar stars, forming the category of Be stars.


Thanks to the XRISM mission, an answer has emerged. Its high-precision observations revealed the presence of a compact companion, likely a white dwarf, which is gradually siphoning matter from Gamma-Cassiopeiae. This discovery closes a chapter of speculation and validates a theory long debated in the astronomical community.

White dwarfs, remnants of stars that have exhausted their nuclear fuel, can, in close orbit, attract and consume gas from massive stars. This process generates the detected X-rays, finally explaining why Gamma-Cassiopeiae shines so brightly in this energy range, as indirectly confirmed by Yaël Nazé from the University of Liège.

Even though these stellar pairs are infrequent, they open new avenues for understanding the evolution of binary systems. Researchers can now refine their models to understand how stars interact and exchange matter over time.