What percentage of their lives do stars spend in the main sequence stage?

Stars spend a significant portion of their lifetimes in the main sequence stage, where they undergo nuclear fusion of hydrogen into helium in their cores. This stage is crucial for a star's development, stability, and energy output, representing a balanced phase in which the inward gravitational force is counteracted by the outward pressure from nuclear fusion.

Typically, astrophysical models show that stars can spend approximately 90% of their lives in this main sequence phase. Smaller stars, like red dwarfs, can remain in the main sequence for tens to hundreds of billions of years, while more massive stars may only spend a few million years in this phase. This means that the main sequence is a dominant phase in stellar evolution, allowing stars to radiate energy steadily and maintain stable characteristics throughout most of their lifespan.

This information supports why the answer stating 90 percent is correct, reflecting a general consensus regarding stellar lifetimes across different star classifications.