A stellar giant is changing its appearance before our eyes, offering a privileged view of the final episodes of its life.
This star, named WOH G64, is located in the Large Magellanic Cloud, a neighboring galaxy. In terms of size, mass, and brightness, it surpasses our Sun. Since 2014, scientists have observed a change in its hue, shifting from red to yellow, indicating a rise in temperature at its surface. This evolution signals that it is gradually transforming into a very particular type of celestial body.
Representation of the binary system WOH G64 surrounded by a dense dust ring.
Credit: Daniel Cea Martinez
This new phase, called a yellow hypergiant, remains extremely brief on a cosmic scale. Only a few dozen examples are recorded in our galaxy. For such a transition to occur, the star must shed its outer layers via powerful stellar winds. This phenomenon, observed here in a rapid and continuous manner, differs from the abrupt transformations usually associated with massive stars.
Moreover, research has shown that WOH G64 is not alone. It actually forms a stellar pair with another star. This discovery makes the explanation of its metamorphosis less obvious. Indeed, the interaction between the two celestial bodies, whether through matter transfer or envelope ejection, could hasten the evolution of the primary star. Astronomers are examining this hypothesis, without ruling out the possibility of an internal mechanism.
Artistic vision of WOH G64: on the left as a red supergiant until 2013, on the right as a binary system with a yellow hypergiant and a hot star since 2014.
Credit: Patryk Iwanek/OGLE The precise origin of this transformation remains to be established. For the team led by Gonzalo Muñoz-Sanchez, it is difficult to determine whether the changes are due to the stellar companion or to processes intrinsic to the star. This uncertainty has consequences for predictions regarding the final destiny of WOH G64, which could end its life in a supernova or directly collapse into a black hole.
The continuation of its evolution could unfold on a relatively short astronomical timescale, from a few hundred to a few thousand years. Although its ultimate explosion is unlikely in our lifetime, the current observation remains valuable. It improves our understanding of the life cycle of massive stars and the phenomena accompanying their end.