What defines the main sequence stage of a star's life?
Answer
The continuous fusion of hydrogen into helium deep within the stellar core
The main sequence is characterized by a stable equilibrium maintained by hydrogen fusion occurring uniformly throughout the star's core, converting hydrogen into helium.

Frequently Asked Questions
What defines the main sequence stage of a star's life?What mechanism immediately takes dominance in a star after core hydrogen fusion ceases?What is the physical process known as hydrogen shell burning?Why does a star evolve into a Red Giant after core hydrogen exhaustion?What causes the visible color shift to red during the Red Giant phase?What is the approximate core temperature required to initiate helium fusion?What is the specific nuclear reaction process that fuses helium nuclei into carbon?In stars similar to the Sun, what specific event characterizes the onset of stable core helium fusion?How does the track of a Red Giant appear on the Hertzsprung-Russell (H-R) diagram?Which evolutionary path is characteristic of stars significantly more massive than the Sun after hydrogen exhaustion?