Submitted by PHealthy t3_124xb33 in askscience
GnarlyNarwhalNoms t1_je1q363 wrote
Reply to comment by Walmsley7 in Is NaCl relatively common in the galaxy/universe? by PHealthy
Yes, the luminousity of a star (which is a direct consequence of "units of matter fused per second") goes up as greater than the cube of mass, about M^(3.5). That means that even though they contain a lot more fuel, they burn through it far more quickly. So for example, a star with two solar masses has roughly twice as much fuel* as the sun, but it burns around 13 times as fast, so its lifespan is less than one sixth of the sun's, or maybe around 1.5 billion years**
So if you plug in a star with, say, 20 solar masses, all of a sudden, you're looking at a lifespan of a small fraction of a billion years.
* It gets a bit more complicated in that large and medium stars have a radiative zone at the core (high pressure supressing convection) underneath a convective zone at the surface. Small stars, smaller than the sun, are entirely convective, meaning that they can use the fuel from the entire stellar mass. Large stars have smaller convective zones which don't interface with the core, meaning that they can run out of fuel even if there's a substantial amount of hydrogen in the upper layers of the star. This is why using mass to calculate star lifetimes isn't as simple as using the entire star's mass to look at how much fuel will be fused. This is also why red dwarf stars have exceedingly long lifespans.
**These are highly handwavey numbers, don't check me on it, but you get the gist.
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