[Mesa-users] epoch-dependent G

[Marco Pereira]

Dear Francis and Mesa-Users,

In the past, it seems that epoch-dependent G investigated only small
variations.
Article a) tried to test a variable G but did so while trying to keep G
constant.  They didn't explore my option.
Article b) just proposed that the Sun was more massive but lost mass
through solar winds (a diet).
So, what I am proposing is distinct and hasn't been done yet, as far as I
can tell.

a) Can a variable gravitational constant resolve the Faint Young Sun
Paradox?
Varun Sahni, Yuri Shtanov
https://arxiv.org/abs/1405.4369


*b) Assessing the massive young Sun hypothesis to solve the warm young
Earth puzzleDavid A. Minton, Renu Malhotra*
https://arxiv.org/abs/astro-ph/0612321

#######################################################
I would like to investigate large variations of G.

I want to calculate G to be inversely proportional to the 4D radius of the
Universe (inverse of the epoch).  This means that G would be 1.5 the
current G0.  That would work if the Sun started as 46% of the current Sun
mass and accreted 9% every billion years.
Of course, the whole galaxy would also have a radius that was 0.46 the
current radius. Angular momentum conservation would have the sun rotating
twice as fast around the galaxy. The hydrogen density would also be around
300% higher.

So, I would like to increase the rate at which hydrogen is accreted into
the sun, have a variable derivative for G, and start with a smaller mass.

So, that is what I would like to try. This is the back-of-envelope
calculation. We all know that the sun loses mass through solar wind.  The
sun should gain mass from falling hydrogen.
[image: image.png]

I will dig deeper into your suggestions. If anyone wants to help me do the
calculation, I would be more than grateful.

Cheers,

Marco Pereira


On Tue, Oct 4, 2022 at 5:00 PM Francis Timmes <fxt44 at mac.com> wrote:

> hi marco,
>
> the topic of variable G arises every now and then. one example is
>
> https://lists.mesastar.org/pipermail/mesa-users/2022-February/013504.html
>
> and
>
>
> https://docs.mesastar.org/en/release-r22.05.1/using_mesa/extending_mesa.html#using-the-other-hooks
>
> https://docs.mesastar.org/en/release-r22.05.1/
>
> seem relevant.
>
> fxt
>
>
>
>
>
>
> > On Oct 4, 2022, at 12:56 PM, Marco Pereira via Mesa-users <
> mesa-users at lists.mesastar.org> wrote:
> >
> > Hi,
> >
> > I installed MESA-r22.05.1 and its SDK.  I finally was able to install
> the program and create the Dox folder using doxygen.
> > So, I am ready to try to understand the program.  That said, what I want
> to do might be quite localized.
> > I want to add into the integration step the knowledge of the value of G
> (Newton's Gravitational Constant) at that time.
> >
> > Any guidance would be much appreciated.  Also, what I have (oxygen HTML
> files) doesn't see to be documented enough for me to understand the program
> with just that.
> >
> > Where can I find broader information on what each module and each file
> does?
> >
> > That said, my thirst for knowledge might not be relevant if the
> epoch-dependent G can be surgically added.
> >
> > Thank you in advance for your help,
> >
> > Marco
> > _______________________________________________
> > mesa-users at lists.mesastar.org
> > https://lists.mesastar.org/mailman/listinfo/mesa-users
> >
>
>
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