ISTANBUL

Astronomers have solved a 50-year mystery surrounding the star Gamma Cassiopeiae, identifying the source of its unusually intense X-ray emissions as a hidden white dwarf companion, according to a study published Wednesday in the journal Astronomy & Astrophysics.

Visible to the naked eye in the Cassiopeia constellation, Gamma Cassiopeiae has long puzzled scientists by emitting X-rays far hotter and more powerful than expected from a typical massive star.

In 1866, Gamma Cassiopeiae became the first Be-type star to be identified. Be-type stars are fast-rotating massive stars that eject matter, forming a disc around the star.

A century later, astronomers found it was about 40 times brighter in X-rays than comparable massive stars, with plasma heated to more than 100 million degrees.

However, using the Resolve instrument aboard Japan’s XRISM space telescope, researchers found that the extreme radiation is produced by a hidden white dwarf drawing in surrounding material and heating it to extraordinary temperatures.

"It is, in fact, the first direct evidence that the ultra-hot plasma responsible for the X-rays is associated with the compact companion, and not with the Be star itself," said Yael Naze, an astronomer at the University of Liege and one of the study’s authors, in a press release.

The findings not only resolve a long-standing astronomical puzzle but also provide strong evidence for a previously theorized type of binary star system.

"Solving this mystery therefore opens up new avenues of research for the years to come," said Naze. "Understanding the evolution of binary systems is crucial for comprehending, for example, gravitational waves, as it is indeed massive binaries that emit them at the end of their lives."