Astronomy clicker question: type II supernova energy source

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

Astronomy 10 learning goal M3.4

Students were asked the following clicker question (Classroom Performance System, einstruction.com) in the middle of their learning cycle:

[0.3 points.] A supergiant will eventually explode as a type II supernova. What provides the energy for this explosion?
(A) Radioactive decays of unstable heavy elements.
(B) Fusion of light elements into heavy elements.
(C) Sudden gravitational contraction.
(D) Dark energy.

Correct answer: (C)

Student responses
Section 4160
(A) : 5 students
(B) : 9 students
(C) : 13 students
(D) : 3 students

Section 5166
(A) : 7 students
(B) : 16 students
(C) : 25 students
(D) : 6 students

Response (D) is merely a ruse (as it had not yet been covered yet in this course sequence). Response (A) is fission, which is not a source of energy for a star. Response (D) is fusion, which can no longer provide energy for a star at the end of its supergiant phase, as it core is iron at this point, past which requires more energy to be put in than can be released by fusion. Thus with no energy source to balance gravity, the core undergoes runaway contraction (becoming a neutron star in the process), and the resulting energy from this gravitational collapse of the core is transferred to the outer layers of the supergiant in an "implosion-explosion" sequence--a type II supernova.

Previous post: Type II supernova simulators.