Heavy Elements in the Sun


by pzona
Tags: elements, heavy
pzona
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#1
Jan6-10, 06:09 PM
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I was reading something the other day on spectral readings from the sun, and I have a few questions regarding its composition.

I know that there are heavier elements (gold, uranium, etc.) in the sun. I'm confused by this, as I didn't think there was enough energy to form such elements. My knowledge of nuclear fusion is pretty limited, although I understand the very basic concepts of it. Do these elements actually form in our sun? Or are they leftover from a supernova in the past?

I also understand from the solar spectrum that lower mass nuclei form in the sun, such as sodium. Is there really enough energy to form such elements, and if so, in what amounts are they present?

I apologize for my lack of knowledge on this, but it's kind of contradictory to what I thought I knew before. I took an astronomy course senior year in high school and it gave me the impression that helium and maybe carbon were the heaviest elements our sun could produce, so I'm a little confused by this. Thanks in advance for any answers.
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sylas
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Jan6-10, 06:37 PM
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Quote Quote by pzona View Post
I was reading something the other day on spectral readings from the sun, and I have a few questions regarding its composition.

I know that there are heavier elements (gold, uranium, etc.) in the sun. I'm confused by this, as I didn't think there was enough energy to form such elements. My knowledge of nuclear fusion is pretty limited, although I understand the very basic concepts of it. Do these elements actually form in our sun? Or are they leftover from a supernova in the past?

I also understand from the solar spectrum that lower mass nuclei form in the sun, such as sodium. Is there really enough energy to form such elements, and if so, in what amounts are they present?

I apologize for my lack of knowledge on this, but it's kind of contradictory to what I thought I knew before. I took an astronomy course senior year in high school and it gave me the impression that helium and maybe carbon were the heaviest elements our sun could produce, so I'm a little confused by this. Thanks in advance for any answers.
The educational website suntrek.org gives some easy introduction to the Sun useful for schools. See, for example, Gold in the Sun? which describes the amount (proportionally tiny; total mass considerable; origin not addressed on this page).

The composition of the Sun is described in What is the Sun made of? (fingerprints), and the origins are addressed in What is the Sun made of? (sun as a star). I suppose it is possible an occasional lucky break would form a heavier atom than usual, but almost all such atoms are from the original dust cloud that formed the solar system. They were formed in turn in other more violent stars. Supernovae certainly make heavy elements and spread them through the galaxy, intermediate weight elements like carbon or oxygen are also made in large stars and can be blown out in planetary nebulae without going supernova.

The heavy elements in planets are formed the same way, and are older than the solar system.

We are, in a real sense, made from dust of ancient stars.

Cheers -- sylas
Astronuc
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Jan6-10, 07:52 PM
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Here's an interesting paper.
The chemical composition of the Sun and the solar system

Solar abundances of the elements

We know that the conditions in the sun are not favorable for the production of heavy elements, therefore it stands to reason that any heavy elements that formed would have been present before the sun was formed, i.e., in the primordial cloud of hydrogen and trace gases that comprise the bulk of the sun.

Photosphere Composition:
Major elements: H - 90.965%, He - 8.889%
Minor elements (ppm): O - 774, C - 330, Ne - 112, N - 102, Fe - 43, Mg - 35, Si - 32, S - 15
Ref: http://nssdc.gsfc.nasa.gov/planetary...t/sunfact.html

http://csep10.phys.utk.edu/astr162/l...mposition.html
http://csep10.phys.utk.edu/astr162/lect/index.html

The heavy elements are rather rare in the cosmos
http://physics.uoregon.edu/~jimbrau/...er21.html#form

pzona
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Jan6-10, 08:22 PM
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Heavy Elements in the Sun


Thanks to both for your prompt responses. These links look very helpful, hopefully I get a chance read them thoroughly over the next few days. I appreciate the help.
Matterwave
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Jan10-10, 08:56 PM
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Nuclear fusion produces elements up to Iron(in very massive stars only - our Sun only produces Helium at this point, and will produce carbon when it expands to a red giant in ~5 billion years).
Beyond that, the R and S-process of neutron capture create the rest of the elements. The process is basically that neutrons are shot out and atoms capture them. The new atoms are unstable and decay to form different elements.
The R process is the rapid process which occurs very fast during a supernova when an atom gets bombarded with neutrons (often taking on 10-20 neutrons before it has a chance to decay) and then decaying to form different elements.
The S process is the slow process which occurs when an atom captures a neutron every once in a while and then decays before it captures other neutrons.
Chronos
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Jan10-10, 10:03 PM
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The short answer is every atom heavier than carbon was present before the sun formed, as noted by others.
joddem
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Aug18-11, 12:58 PM
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I don't see how "lucky breaks" would be possible. While fusion of elements lighter than iron results in generation of energy, fusion of heavier elements requires the consumption of energy. Lucky breaks could cause stars to move on main sequence of the HR diagram, which does not happen. Once a star is on the main sequence it stays in place on the main sequence. Heavy elements are formed exclusively in supernovae (both types I and II) and possibly hypernovae. If someone could explain to me what the error in my reasoning is if in fact lucky breaks are possible, I would be interested.
Integral
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Aug18-11, 03:10 PM
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The composition of the sun is a current hot topic and there have been some significant changes in what we belive. See

M.Asplund et al. "The chemical composition of the sun." Annual Review of Astronomy and Astrophysics. 2009

Though there is not yet a consensus it seems that
H 71.5%
He 27%
Metals (ie everything else) 1.4%

The amounts of C, N, O, Ne are are part metals and exact ratio depends upon who you talk to.

Science News Aug 2010
turbo
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Aug18-11, 03:36 PM
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In Astronomical parlance, "metals" in stars means any elements heavier than helium. So it's best to try to nail down the proportions of those elements that we can detect through spectroscopy. In practice, I'm not aware of any star that doesn't have some degree of metallicity.


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