Animation showing the evolution and mass transfer in a massive binary system. It illustrates the key stages of the process: the more evolved star, having expanded, transfers helium-rich gas to its companion, altering the chemical composition of the latter’s surface. The complete sequence shows how this cycle subsequently culminates in the violent supernova explosion of the donor star, a cataclysm that drastically reshapes the system’s orbit or may even destroy it entirely. Credit: Gabriel Pérez Díaz (IAC).