[mesa-users] A common stellar-structure myth

[RICHARD H D TOWNSEND]

Ideal gas, hydrostatic equilibrium plus radiative diffusion for a constant opacity — combine together, and one finds that L ~ M^3. This scaling fits the main sequence reasonably well.

cheers,

Rich

> On Aug 30, 2016, at 5:20 PM, Brian Jackson <bjackson at boisestate.edu> wrote:
> 
> Since we're reviewing basic stellar evolution, can I ask why L ~ M^3?
> That just comes from the equation of state?
> 
> Thanks,
> Brian
> 
> On Tue, Aug 30, 2016 at 4:17 PM, RICHARD H D TOWNSEND
> <townsend at astro.wisc.edu> wrote:
>> That’s as maybe, but the gravity is not stronger.
>> 
>> In any case, what really drives the large energy generation rate in massive stars is the energy loss rate through the stellar surface, which scale as L ~ M^3 (independent of nuclear reactions). The pre-MS star continues to contract until the core energy generation rate matches this loss rate.
>> 
>> cheers,
>> 
>> Rich
>> 
>>> On Aug 30, 2016, at 5:05 PM, Tomasz Plewa <tomekplewa at gmail.com> wrote:
>>> 
>>> It's a deeper potential well.
>>> 
>>> Tomek
>>> --
>>> 
>>> 
>>>> On Aug 30, 2016, at 5:52 PM, RICHARD H D TOWNSEND <townsend at astro.wisc.edu> wrote:
>>>> 
>>>> Hi folks —
>>>> 
>>>> While reading the textbook I’m going to be teaching from this semester (“Pathways to Astronomy”, by Schneider & Arny), I came across this common myth about stellar structure:
>>>> 
>>>> “The stronger gravity of a more massive star drives up the rate of nuclear fusion dramatically, while smaller stars consume their fuel at a more leisurely pace”.
>>>> 
>>>> The attached figure, courtesy of MESA, shows the internal gravity for 1Msun and 10Msun stars at the ZAMS — and nicely busts the myth.
>>>> 
>>>> cheers,
>>>> 
>>>> Rich
>>>> 
>>>> <gravity.pdf>
>>>> ------------------------------------------------------------------------------
>>>> _______________________________________________
>>>> mesa-users mailing list
>>>> mesa-users at lists.sourceforge.net
>>>> https://lists.sourceforge.net/lists/listinfo/mesa-users
>> 
>> ------------------------------------------------------------------------------
>> _______________________________________________
>> mesa-users mailing list
>> mesa-users at lists.sourceforge.net
>> https://lists.sourceforge.net/lists/listinfo/mesa-users
> 
> ------------------------------------------------------------------------------
> _______________________________________________
> mesa-users mailing list
> mesa-users at lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/mesa-users