The binary star system β Lyrae (also known as Sheliak) consists of a 2.97 solar mass giant star orbiting a 13.16 solar mass main sequence star. What about this system is surprising? Explain how this system came to be, and how this system will likely evolve in the future.
What is surprising about the β Lyrae binary star system is the significant mass difference between the two stars. In a typical binary star system, the two stars would have similar masses. However, in this case, the giant star is almost three times less massive than the main sequence star.
This system likely formed from a binary star progenitor, where two stars formed from the same molecular cloud. As they evolved, the more massive star entered its giant phase, expanding and transferring mass to its companion through stellar winds. This mass transfer process likely resulted in the giant star losing most of its original mass, while the main sequence star gained additional mass, leading to the current mass disparity.
In the future, the system will continue to evolve. The giant star will continue to transfer mass to the main sequence star, which will further increase its mass. As the mass of the main sequence star increases, it will eventually also enter its giant phase, and the mass transfer process may reverse. This evolutionary stage is known as a common envelope phase, where the two stars share a common envelope of gas.
During the common envelope phase, the outer layers of the giant star are ejected, and the core of the giant star and the main sequence star become close together, orbiting inside the common envelope. This phase is highly unstable, and the interaction between the stars and the envelope causes the orbital separation to decrease rapidly, eventually leading to the merger of the two stars or the formation of a close binary system.
The exact outcome of the future evolution of the β Lyrae system is uncertain and depends on various factors like the masses and orbital parameters of the stars. It is possible that the stars may merge, forming a more massive single star or a rapidly rotating star. Alternatively, they may continue to orbit each other as a tight binary system. These future scenarios are still subject to ongoing research and observations.