What process allows Red Dwarfs (less than $0.5 M_{\odot}$) to achieve lifespans exceeding the current age of the universe?

Answer

Convection continuously stirs fresh hydrogen into the core

The exceptionally long lifespans predicted for low-mass Red Dwarfs, potentially lasting for trillions of years, stem from their highly efficient fuel usage mechanism involving convection. Unlike solar-mass stars where hydrogen burning is confined to a central core, Red Dwarfs are largely convective throughout their structure. This process acts like continuous stirring, bringing fresh, unused hydrogen from the outer layers down into the fusion region. This allows the star to utilize nearly 100% of its total hydrogen content over vast timescales, contrasting sharply with more massive stars where only a small central fraction is accessible during the main sequence phase.

What process allows Red Dwarfs (less than $0.5 M_{\odot}$) to achieve lifespans exceeding the current age of the universe?

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