[mesa-users] A common stellar-structure myth

[Alexander Heger]

Dear Richard,

I tend to agree with Tomek.
It seem not obvious that gravity refers the acceleration rather than
potential.
Obviously, acceleration is zero in the centre of both stars, yet burning is
largest there.
;-)

Compare pressures.

-Alexander

On 31 August 2016 at 08:26, RICHARD H D TOWNSEND <townsend at astro.wisc.edu>
wrote:

> 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>
> >>>> ------------------------------------------------------------
> ------------------
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