Earliest stars

This is a nice piece.

This is a moving target right now but check decent sites and follow up with papers.

https://phys.org/news/2024-02-stars-impact-galaxies.html

 

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I read that. 2 questions:

- I didn't see any explanation of why "metals" , i.e. elements heavier than H, He, cause faster cooling of gas clouds. Do you know?

- Their modelling seems to assume there is something called a dark matter halo surrounding all this activity. I presume that dark matter, being electromagnetically inactive, is unaffected by all these processes except the movement of mass, which will exert some gravitational effect on it. So the shock front of an exploding supernova, for example will barely cause it to change position at all. Very counterintuitive.

 

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Just a guess but:
- a uranium atom being kicked out of a gas cloud takes with it about 238 times more kinetic energy than a hydrogen atom.
- a uranium atom is about six times larger than a hydrogen atom and is therefore statistically more likely to get kicked

 

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Metals are more effective than hydrogen and helium at radiating thermal energy.

 

That may be an aggregate property; I'm not sure how much that applies to unbonded individual atoms.

 

Why, though?

 

I would have thought not. Won’t all atoms of a monatomic gas at thermal equilibrium regardless of their mass, contribute 1/2 kt per degree of freedom to the specific heat?

 

Metals cool more effectively than hydrogen due to their radiative cooling properties, even though both contribute equally to specific heat.

 

How does that arise? Why would heavier elements radiate more, at a given temperature? Wouldn’t they have the same black body curve?

 

Not in terms of thermodynamics explicitly. Intuitively? The way I read it.
Larger mass can absorb heat more efficiently than lighter atoms.
We have the CMBR which would have been a lot hotter in the first few hundred million years but if exclude that and just take the thermal radiation from the Pop 3 stars.
H and He is heated excited in the galaxy via this radiation which increase kinetic energy of the gas. The star goes SN throwing out atoms heavier than H/He which absorb some of that kinetic energy like throwing sand on a fire.

That is the way I imagine it but that could be wrong. I have only read the article not the paper which will be above my pay grade.

As a chemist from a thermodynamic perspective how would you approach it?

EDIT: Just checked and It's the abstract only, plus this work is based on computer models which I don't know anything about.
They plug in A and B and it spits out C. 1. How good is the model? How accurate is the data they plug in?
I think the process is interesting, pop 3 then SN leads to more star formation. If this is the way it happened then this could partly explain why they found so many early galaxies with higher mass and higher structure.

Possibly...

 

See some of my above comments. I struggle, hence my question.

I wonder if it may be something to do with radiation at a wider range of wavelengths, i.e. not just black body but a wider range of specific emission bands, or something like that. Perhaps if I have time I'll go hunting on the internet for an answer.

 

The article mentioned UV specifically from the pop 3 stars but there would be surely more as stars throw out a whole lot more.
Our sun is a Pop 1 I assume (I'll check) it's SPD covers all optical plus UV and IR. Those coronal emissions that interfere with our coms from time to time may have higher energy. I'll check.

 

Anything involving DM, I have no idea. Part of the cosmic web, backbone, around galaxies, most of the mass of the universe, yet no hint at the LHC.

 

There is a string of publications in this link but they are 10-20 years old. All pre JWST.

Pop 3 stars, emissions and other stuff. Where is an astrophysics expert when you need one!

https://www.sciencedirect.com/topics/physics-and-astronomy/population-iii-stars

I don't recognise all the journals so may not be kosher.

 

Is it dark matter gravitationally churning (changing densities and velocities) within normal matter clouds, and so forcing that normal matter into reactions within itself / cloud?

Why metals good at cooling here? My (ignorant) guess, metals having more electrons will be prone to losing energy via the reactions.
DaveC42’s post gave me the idea.

 

Let's ask one of our LLM friends...

"
Heavier elements, despite having the same black body curve, can indeed radiate more energy at a given temperature. Let’s explore why:

1. Black Body Radiation:
   
   • A black body is an idealized object that absorbs all incident radiation and emits radiation based solely on its temperature.
   • The black body curve (also known as the Planck curve) describes the distribution of radiation emitted by a black body at different wavelengths.
   • According to Planck’s law, the intensity of radiation from a black body depends on its temperature and the wavelength of the radiation.
2. Wien’s Displacement Law:
   
   • Wien’s law states that the peak wavelength of the black body curve (where intensity is highest) is inversely proportional to the temperature.
   • Mathematically, (\lambda_{\text{max}} \propto \frac{1}{T}), where (\lambda_{\text{max}}) is the peak wavelength and (T) is the absolute temperature.
3. Why Heavier Elements Radiate More:
   
   • Atomic Structure: Heavier elements have more complex atomic structures with additional energy levels and electronic transitions.
   • Transition Frequencies: These additional energy levels allow heavier elements to undergo a wider range of electronic transitions.
   • Emission Lines: When electrons transition between energy levels, they emit radiation at specific wavelengths (characteristic emission lines).
   • Continuous Spectrum: In addition to these lines, heavier elements also contribute to the continuous part of the black body spectrum.
   • Higher Intensity: The combination of emission lines and continuous radiation results in a higher overall intensity (more energy emitted) compared to simpler elements like hydrogen.
4. Example: Iron vs. Hydrogen:
   
   • Consider iron (a heavier element) and hydrogen (the lightest element).
   • At the same temperature, iron emits a broader spectrum of radiation due to its complex electronic transitions.
   • While both elements follow the same black body curve, iron’s overall intensity (total energy radiated) is greater.
5. Applications:
   
   • These principles apply not only to stars but also to various astrophysical phenomena, such as the spectral lines observed in stellar spectra.
   • Elements like iron, oxygen, and carbon contribute significantly to the overall radiation from stars.

In summary, while the black body curve remains the same, the complexity of heavier elements’ atomic structure allows them to radiate more energy across a broader spectrum, enhancing their overall intensity. "

 

Aha, so this is the mechanism I wondered about in post 11, then. Thanks.

By the way, who are these "LLM friends" and where are you quoting this from?

 

I was just using Bing Chat (Copilot)... so take anything that doesn't ring true to you with a grain of salt.

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Oh shit so that's pretty worthless then. And I don't suppose it tells you where it got it from?

 

Sometime there are footnoted sources and sometimes not. Just for fun I asked for it this time and rather than footnoted statements it just gave the following.


Certainly! Here are some sources that provide further insights into why heavier elements radiate more efficiently than hydrogen:

1. Physics Stack Exchange:
   • In this discussion, experts explain why elements heavier than helium (collectively termed “metals” in astrophysics) are more opaque and radiate more efficiently.
   • The complexity of electron orbital structures and available transitions in heavier elements contributes to their enhanced radiative cooling.
   • Read more1.

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1. ScienceAlert:
   • This article discusses how ancient stars forged elements heavier than anything found in nature.
   • It highlights the role of fusion processes in creating heavier elements, including iron.
   • Read more2.

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1. National Radio Astronomy Observatory (NRAO):
   • The NRAO explains how elements heavier than helium are formed.
   • Supernova explosions and neutron star mergers are key processes for creating heavy elements.
   • Read more3.

In summary, these sources provide valuable information about the radiative properties of heavier elements and their impact on stellar evolution.