Astronomy quiz question: CNO cycle stars

Astronomy 10 Quiz 9, Spring Semester 2007
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q9.4

[3.0 points.] Which one of the following choices best explains what allows hydrogen to fuse together with much heavier elements in the cores of massive main sequence stars?
(A) Stronger gravitational forces.
(B) Stronger degenerate pressures.
(C) Continuous absorption and reemission of higher energy photons.
(D) Higher temperatures.
(E) Stronger convection currents.

Correct answer: (D)
Higher temperatures mean faster speeds. For hydrogen fusion, the temperature must be high enough for protons to approach close enough to fuse, in spite of the mutually repulsive force due to their positive charge. For hydrogen to fuse together with a heavier element (such as carbon, which has 14 protons), the temperature must be even higher for the hydrogen proton to approach the stronger repelling carbon nucleus.

Student responses
Section 4136
(A) : 18 students
(B) : 6 students
(C) : 3 students
(D) : 2 students
(E) : 10 students

Student responses
Section 5076
(A) : 5 student
(B) : 2 students
(C) : 3 students
(D) : 10 students
(E) : 1 students