Astronomy quiz question: compact object with accretion disk

Astronomy 210 Quiz 6, spring semester 2014
Cuesta College, San Luis Obispo, CA

A __________ with a companion star can have a glowing x-ray accretion disk.
(A) white dwarf.
(B) neutron star.
(C) black hole.
(D) (Two of the above choices.)
(E) (All of the above choices.)
(F) (None of the above choices.)

Correct answer (highlight to unhide): (E)

Depending on the initial mass of the compact object--whether a very massive star, a massive star, or just a slightly more massive medium-mass star--this compact object could be a black hole, neutron star, or white dwarf. In all these cases, the compact object would have completed its stellar evolution faster than and be sufficiently close enough to its companion star (that would have been a medium-mass star that has just finished its main-sequence lifetime to become a giant) to accumulate hydrogen from its expanding outer layers.

This infalling hydrogen collects into an accretion disk surrounding the companion star, and due to Kepler's third law, the outer part of the disk orbits slower than the inner part of the disk. Due to the density of the disk, the difference in speeds between adjacent parts causes friction, producing enough heat for the disk to become incandescent, thus emitting blackbody radiation that peaks in the x-ray portion of the electromagnetic spectrum.

Section 30674
Exam code: quiz06n0mM
(A) : 3 students
(B) : 8 students
(C) : 6 students
(D) : 4 students
(E) : 4 students
(F) : 0 students

Success level: 21% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.27