Question

What has to happen for a star to join the main sequence ?

1) Nuclear Fusion

2) Shell Heating

3) Use up most of its available fuel

4) Hydrostatic Equilibrium

Answer 1

Nuclear fusion

Step-by-step explanation:

This is because main sequence of star is powered by fusion of hydrogen to helium atoms together and this process releases energy. The energy released when the gas collapse into a protostar make the center of the protostar to be extremely hot. When the core becomes very hot, nuclear fusion can start.