Astronomy quiz question: black holes with companion stars

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

Astronomy 10 learning goal Q10.3

[3.0 points.] Which one of the following statements best explains why x-rays are observed from close binary systems comprised of black holes with companion stars?
(A) Only x-ray photons are fast enough to escape from black holes.
(B) Electrons falling into lower energy orbitals release x-ray photons.
(C) Black holes can only emit x-ray photons.
(D) Accretion disks surrounding black holes emit very hot blackbody radiation.
(E) Companion stars orbiting black holes emit very hot blackbody radiation.

Correct answer: (D)

A companion star of a black hole may be close enough such that it will overflow its Roche lobe when it becomes a giant or superigant, thus transferring hydrogen to the black hole. This infalling hydrogen collects into an accretion disk surrounding the black hole, heating up in the process to become incandescent, emitting blackbody radiation.

Student responses
Section 4160
(A) : 3 students
(B) : 5 students
(C) : 6 students
(D) : 16 students
(E) : 4 students

Previous post:
Astronomy in-class activity: compact objects with companion stars.