[Mesa-users] epoch-dependent G

Sun Oct 9 21:05:04 UTC 2022

Dear Francis,

Thank you very much for your help.  I finally understood what you said.

Marco

On Sun, Oct 9, 2022 at 2:32 PM Francis Timmes <fxt44 at mac.com> wrote:

> i repeat that using the other_cgrav hook propagates G correctly through
> mesa/star,
> be that change in G "large" or "small", variable in space or time, or
> dependent on other variables.
>
>
> https://docs.mesastar.org/en/release-r22.05.1/using_mesa/extending_mesa.html#using-the-other-hooks
>
> fxt
>
>
>
>
>
> > On Oct 9, 2022, at 6:29 AM, Marco Pereira <ny2292000 at gmail.com> wrote:
> >
> > Dear Francis and Users,
> >
> > I sought files where the word grav was mentioned.  My goal is to just
> add a time-dependent G to the evolution of Stars.
> > I found do_evolve_one_step method in run_star_support8.f90.  I suspect
> that that is where I should make my modifications.
> > I also know that grav will affect star winds and star oscillations
> frequencies (gyre).
> >
> > In addition, to star evolution, I recognize the study of binary systems
> in the package is also relevant since I did simple modeling of type 1a
> Supernovae to get their Absolute Luminosity G-dependence as G^{-3.33}
> >
> > Attached is the full list of mentions of the word "grav" and the files
> where they are located.
> >
> > My naive expectation was that there would be a nuclear chemistry
> propagator (where the nuclear chemistry rate equations would be propagated
> step by step taking into consideration density and composition). I thought
> that that would be connected to the evolve_one_step method. The other
> relevant point would be the calculation of the star winds since they would
> push away the feeding hydrogen cloud. That should account for a smaller
> initial mass and larger G.  That is relevant because in my model the
> initial mass of the sun is around 47% of the current mass and the
> pushed-away gas cloud would fall back into the star over 4 billion years.
> > So, my model adds a falling hydrogen cloud to the modeling of the sun.
> >
> > Any comments would be welcomed.  At this exact moment, I am still
> incapable of stepping (debugging) through this Fortran program and so I am
> not quite sure where it goes. In fact, I have CLion and code::blocks. How
> do people debug this program?
> >
> > Thanks,
> >
> > Marco
> >
> > On Tue, Oct 4, 2022 at 7:45 PM Marco Pereira <ny2292000 at gmail.com>
> wrote:
> > The hydrogen density would also be around 10 times higher.
> >
> > On Tue, Oct 4, 2022 at 7:01 PM Marco Pereira <ny2292000 at gmail.com>
> wrote:
> > 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 puzzle
> > David 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.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
> > >
> >
> > <FoundGrav.txt><FoundGravFiles.txt>
>
>
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