Astronomy quiz question: mass transfer in close-pair binaries

Astronomy 10 Quiz 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q10.2

[3.0 points.] Which one of the following statements best explains why the transfer of hydrogen in a close-pair binary system from a less massive star to a more massive star happens very slowly?
(A) There is not much hydrogen left in the less massive star.
(B) They move farther apart from each other.
(C) The less massive star has not yet ended its main sequence lifetime.
(D) The more massive star produces strong winds.
(E) (None of above choices (A)-(D), as it is not possible for hydrogen to be transferred from a less massive star to a more massive star.)

Correct answer: (B)

When a less massive star is transferring hydrogen to a more massive star, their masses become more unequal, such that their separation distance increases. This decreases their orbital speeds, decreasing centrifugal forces, resulting in enlarging their Roche lobes, making it more difficult for the less-massive star to overflow its Roche lobe. This will slow down, and eventually stop the transfer of hydrogen from the less massive to the more massive star.

Student responses
Section 4160
(A) : 11 students
(B) : 11 students
(C) : 6 students
(D) : 1 student
(E) : 5 students

Related post:
Astronomy in-class activity: mass transfer in close-pair binaries.