Expert: Tom Whiting - 6/13/2008

Question
How does the temperature in the core of a star affect the star's lifespan and luminosity?

Answer
With a single star, ALL physical characteristics of the star,
core temperature, surface temperature, lifespan, luminosity,
diameter, color, spectral classification...are dependent and established, with the inital starting MASS.  So MASS is the key number, not the core temperature, which is set by the initial starting mass.

The higher the starting mass, the higher the core temperature
and surface temperature, the shorter the lifespan (because the
higher core temperatures use up the available fuel at a much more
rapid and prodigious rate), and so the brigher the star (luminosity) and the larger the diameter.

This is only true for isolated single stars, and widely separated
multiple stars where there is no interaction with it's partners.
But it does not apply to close doubles where mass transfer between
the partners can occur. This alters the initial mass state of the
star in close, mass transfer, binaries.

Very large massive stars (nature makes only one in a thousand) have such high core temperatures that they use up their available hydrogen fuel at a very rapid rate, thus their lifespans are in the tens of millions of years (very very short lives) and thus they have very high luminosities.  (Average lifespan is only about 10-25 million years).

Very common (the most common star in fact) little red dwarfs, nearly
80% of all stars, are so cool in their cores, they miserly conserve
their available fusion fuel, and have estimated lifespans in the several trillions of years, with very low luminosities.
Their lifespans are so long, we have never witnessed a little red
dwarf star evolve to it's next life stage (whatever it is), having only had 13.7 billion years pass since the beginning Big Bang...we have only just begun, compared to the long lifespan of a little red dwarf star.

The middle stars (solar-type, about 20% of all stars) are in the
middle, like our sun, with average core temperatures, lifespans
in the 6-12 billion year range, and with average luminosities.
(Our own sun has an estimated lifespan of about 10 billion years).

So in conclusion, the bigger the star (mass and diameter wise), the higher the luminosity, the higher the core temperature, and the shorter the lifespan.

That's how they break down, and are classified.
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA