Prior to reaching the main sequence,a protostar's energy comes mostly from
A) gravitation.
B) nuclear fusion.
C) nuclear fission.
D) natural radioactivity.

Question

Quizplus · Accepted Answer

Prior to reaching the main sequence, a protostar's energy comes mostly from gravitational contraction, which heats the gas and dust in the protostellar cloud, causing the temperature and pressure to increase. This process continues until the core of the protostar becomes hot and dense enough for nuclear fusion to begin.

Prior to Reaching the Main Sequence,a Protostar's Energy Comes Mostly