You Discover a Binary Star System in Which One Star

Multiple Choice

You discover a binary star system in which one star is a 15 MSun main- sequence star and the other is a 10 MSun giant. How do we think that a star system such as this might have come to exist?

A) The giant must once have been the more massive star, but is now less massive because it transferred some of its mass to its companion.
B) The two stars are simply evolving normally and independently, and one has become a giant before the other.
C) The two stars probably were once separate, but became a binary when a close encounter allowed their mutual gravity to pull them together.
D) Although both stars probably formed from the same clump of gas, the more massive one must have had its birth slowed so that it became a main sequence stars millions of years later than its less massive companion.