<p>Is there a good source of information of the expected density profile inside a red giant star?</p>
<p>I have read that when a star such as the sun has converted much or most of the hydrogen in its core into helium, generally speaking, the inner 10% of the sun's radius, that core contracts to become even smaller, and it heats up.  This process initiates hydrogen fusion in a shell surrounding the helium core.  Owing to increased hydrogen fusion generating increased heat in a shell surrounding the compressed helium core (which hasn't started fusing much helium, yet!), the outer part of the star expands greatly, and its surface also cools, forming a red giant star.</p>
<p>Is there any scientific literature containing plots of the results of those computer simulations?  The plots of interest are the density with radius, the enclosed mass with radius along with hash marks indicating the extent of the helium core and the surrounding hydrogen-fusing shell.  Maybe such a figure is hard to render in a scientific journal because the hash marks of the core and shell would be microscopic compared with the extent of the envelope when plotted within the page width allowed for a figure?</p>
<p>Whereas the size and luminosity of at least nearby red giant stars is an observable fact, I &quot;get&quot; that the internal structure of such a star is inferred from a lot of math and physics supplied to computer simulations.  From what is written on the topic, I have the impression that paradoxically, the &quot;internals&quot; of a red giant star is a rather compact object surrounded by a large, tenuous envelope, so much so that the outer reaches of such a star are described as &quot;a pretty good laboratory vacuum.&quot;</p>
<p>Yes, a red giant isn't just one thing.  Even for a specified mass, it is an &quot;evolutionary track&quot; on the H-R diagram.  If the information I seek isn't in a figure in a particular paper, how hard is it to run someone's published software code to generate those plots?  I don't want to understand all of the math and physics.  I was wondering if I could write a Web app with sliders to input mass and age leaving the Main Sequence, and if there was a software library I could call to generate those profiles.  I would call this Web page &quot;The Visible Red Giant.&quot;</p>

CC BY-SA 4.0
2022-09-04T06:09:05.740Z
If you want to have sliders to choose input mass and age, seems like one single plot from the literature won't be enough for your purpose. You would need a grid of stars with different masses, and one plot for each of them. This is probably something that is not available in the literature exactly as you would like it. You can see if you want to generate it yourself with the [MESA](https://docs.mesastar.org/en/latest/) code. If I find the time, I will write an answer about that
Prallax
CC BY-SA 4.0
2022-09-04T18:43:59.667Z
different question but perhaps a start [this answer to *Role of power laws in astronomy?*](https://astronomy.stackexchange.com/a/44455/7982) and especially [this answer to *Has stellar evolution ever been modeled analytically?*](https://astronomy.stackexchange.com/a/29820/7982) Not a red giant, but the density profile of our Sun can be seen in [this answer to *What is the density profile within the Sun's photosphere? Which one of these is wrong?*](https://astronomy.stackexchange.com/a/32737/7982) and
uhoh
CC BY-SA 4.0
2022-09-04T18:46:04.047Z
[this answer to *At what depth below the Sun's surface does the density reach that of water?*](https://astronomy.stackexchange.com/a/32734/7982) in Physics SE [*Density of the Sun*](https://physics.stackexchange.com/q/201235/83380) If one can find a polytrope model for a red giant, one can make a density plot.
uhoh
CC BY-SA 4.0
2022-09-06T16:29:59.067Z
Thanks for those answers about the Sun -- they are very detailed and interesting.  Does anyone have something like these results of a "model run" for a representative red giant star?
PAUL MILENKOVIC
<stellar-evolution><red-giant>
Source of information on density profile of a red giant star?
PAUL MILENKOVIC
# Source of information on density profile of a red giant star?

(Asked by: username_0 on 2022-09-04)

Is there a good source of information of the expected density profile inside a red giant star?

I have read that when a star such as the sun has converted much or most of the hydrogen in its core into helium, generally speaking, the inner 10% of the sun's radius, that core contracts to become even smaller, and it heats up. This process initiates hydrogen fusion in a shell surrounding the helium core. Owing to increased hydrogen fusion generating increased heat in a shell surrounding the compressed helium core (which hasn't started fusing much helium, yet!), the outer part of the star expands greatly, and its surface also cools, forming a red giant star.

Is there any scientific literature containing plots of the results of those computer simulations? The plots of interest are the density with radius, the enclosed mass with radius along with hash marks indicating the extent of the helium core and the surrounding hydrogen-fusing shell. Maybe such a figure is hard to render in a scientific journal because the hash marks of the core and shell would be microscopic compared with the extent of the envelope when plotted within the page width allowed for a figure?

Whereas the size and luminosity of at least nearby red giant stars is an observable fact, I "get" that the internal structure of such a star is inferred from a lot of math and physics supplied to computer simulations. From what is written on the topic, I have the impression that paradoxically, the "internals" of a red giant star is a rather compact object surrounded by a large, tenuous envelope, so much so that the outer reaches of such a star are described as "a pretty good laboratory vacuum."

Yes, a red giant isn't just one thing. Even for a specified mass, it is an "evolutionary track" on the H-R diagram. If the information I seek isn't in a figure in a particular paper, how hard is it to run someone's published software code to generate those plots? I don't want to understand all of the math and physics. I was wondering if I could write a Web app with sliders to input mass and age leaving the Main Sequence, and if there was a software library I could call to generate those profiles. I would call this Web page "The Visible Red Giant."

**Tags:** stellar-evolution, red-giant

> **Comments:**
> **username_1**: If you want to have sliders to choose input mass and age, seems like one single plot from the literature won't be enough for your purpose. You would need a grid of stars with different masses, and one plot for each of them. This is probably something that is not available in the literature exactly as you would like it. You can see if you want to generate it yourself with the [MESA](https://docs.mesastar.org/en/latest/) code. If I find the time, I will write an answer about that  
> **username_2**: different question but perhaps a start [this answer to *Role of power laws in astronomy?*](https://astronomy.stackexchange.com/a/44455/7982) and especially [this answer to *Has stellar evolution ever been modeled analytically?*](https://astronomy.stackexchange.com/a/29820/7982) Not a red giant, but the density profile of our Sun can be seen in [this answer to *What is the density profile within the Sun's photosphere? Which one of these is wrong?*](https://astronomy.stackexchange.com/a/32737/7982) and  
> **username_2**: [this answer to *At what depth below the Sun's surface does the density reach that of water?*](https://astronomy.stackexchange.com/a/32734/7982) in Physics SE [*Density of the Sun*](https://physics.stackexchange.com/q/201235/83380) If one can find a polytrope model for a red giant, one can make a density plot.  
> **username_0**: Thanks for those answers about the Sun -- they are very detailed and interesting.  Does anyone have something like these results of a "model run" for a representative red giant star?  

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