You discover a binary star system in which one member is a 15 solar mass main- sequence star and the other star is a 10 solar mass giant star. Why should you be surprised, at least at first?
A)The odds of ever finding two such massive stars in the same binary system are so small as to make it inconceivable.
B)It doesn't make sense to find a giant in a binary star system.
C)The two stars should be the same age, so the more massive one should have become a giant first.
D)The two stars in a binary system should both be at the same point in stellar evolution; that is, they should either both be main- sequence stars or both be giants.
E)A star with a mass of 15 solar masses is too big to be a main- sequence star.

Question

Quizplus · Accepted Answer

The two stars should be the same age, meaning that the more massive star should have evolved into a giant first. However, in this binary system, the less massive star is the giant and the more massive star is still on the main sequence. This is unexpected and requires further investigation.

You Discover a Binary Star System in Which One Member