In which phase of a star's life are thermonuclear reactions converting hydrogen into helium in the core of a star?
A) The main-sequence phase
B) The horizontal branch phase
C) As the star moves up the red-giant branch for the first time
D) The protostar phase

Question

Quizplus · Accepted Answer

Thermonuclear reactions converting hydrogen into helium occur during the main-sequence phase, which is the longest phase in a star's life cycle. During this phase, the star is stable and the energy produced by these reactions counteracts the force of gravity pulling the star inward.

In Which Phase of a Star's Life Are Thermonuclear Reactions