In a binary system, the first star to fill its Roche lobe is usually a red giant. What can we say about the nature of the other star when this happens?
A)There is no correlation between the two stars, so the second star may be at any stage of evolution.
B)The two stars in a binary system must have the same mass, so the second star must be a red giant at this time also.
C)The two stars in a binary system are formed at the same time, so the other star must be a main-sequence star.
D)The two stars in a binary system are formed at the same time, so the other star is most likely still a protostar.

Question

Quizplus · Accepted Answer

When one star in a binary system fills its Roche lobe and becomes a red giant, it indicates that the system is at an advanced stage of evolution. Since binary stars are formed at the same time, the other star should also be evolved, but not necessarily as a red giant. It is most likely a main-sequence star, as red giants have a shorter lifespan than main-sequence stars. Therefore, option C is the best choice as it provides the most accurate information about the nature of the other star in a binary system when one star fills its Roche lobe.

In a Binary System, the First Star to Fill Its