[Mesa-users] epoch-dependent G

Francis Timmes fxt44 at mac.com
Sun Oct 9 18:32:25 UTC 2022


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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