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This whole we're made from stars thing.

  1. Apr 10, 2013 #1
    This whole "we're made from stars" thing.

    I keep coming across internet memes that say all the elements (except H and He) were created from stars, and therefore, humans are the product of stars. Every atom in our body came from a star billions of years ago.

    I never gave it a second thought since obviously humans are created from a sperm and egg, which come from other humans, not stars. Although more and more I keep seeing memes that say this. So, I figured I'd ask about it on here since you guys have a lot more knowledge about this. Am I right in saying that there is no truth to this, or is it factual?
     
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  3. Apr 10, 2013 #2

    phyzguy

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    It is definitely factual. All of the elements heavier than hydrogen and helium were manufactured in stars, as you said. Yes, a human starts out as the union of an egg and a sperm, but where do the elements that make up the egg and the sperm come from? A person then grows by ingesting food. Where do the atoms that make up the food come from? The answer is that all of the elements that make up a person come from the Earth, and the Earth was formed from gas and dust that condensed from a huge cloud of interstellar matter. The elements heavier than hydrogen and helium in this cloud were manufactured in massive stars, which then exploded and scattered these elements throughout the galaxy, where they were available to form the Earth, the sun, and the other planets.
     
  4. Apr 10, 2013 #3

    phinds

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    It is completely factual that every atom in your body EXCEPT H and He was created in a star. The fact that they got there there via a roundabout route does not change that fact.
     
  5. Apr 10, 2013 #4

    collinsmark

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    Actually, this is a bit more complicated than it first sounds.

    Even most hydrogen atoms found commonly found here on earth may have at one time been a part of a star, even it they weren't synthesized within the star. Large stars still contain mostly hydrogen and helium with much heavier elements in their core, up to iron. Eventually it goes supernova, producing even heavier elements. But still, most of that hydrogen and helium is just blown off.

    But even if those atoms were around before the star was formed, they were at one time part of the star. Does that still not make the atoms "former star stuff"?

    It gets more complicated. Let me summarize individual atoms.

    Hydrogen:
    Hydrogen is pretty abundant on Earth in heavier compounds molecules (e.g., water). Most hydrogen atoms here on Earth were created during big-bang nucleosynthesis. That said, those hydrogen atoms might have very likely been part of a star at some point in the past. A [STRIKE]little[/STRIKE] tiny amount of hydrogen here on Earth comes from [STRIKE]radioactive decay[/STRIKE] cosmic/gamma ray/neutron interactions involving of heavier atoms in the upper atmosphere, but I think that's a negligible amount.

    Helium:
    Much of the helium created in the universe was created during big-bang nucleosynthesis, although some can also be produced in stars too. But practically none of that is here on Earth! That's right, nearly all the helium here on Earth is not star stuff!* Most all the helium here on earth is the result of radioactive decay (particularly alpha decay) of heavier elements such as thorium and uranium. The rest of the helium left our atmosphere a long time ago. So all the helium that we interact with (helium balloons for example) was formed relatively recently.
    *(I say "not star stuff," but technically it is the decay products of former star stuff.)

    Lithium:
    the current theory is that most of the lithium (on Earth and in the universe) was created during big-bang nucleosynthesis. The thing about lithium in stars is that it doesn't get produced very much. The nuclear fusion reactions that typically happen in stars skip over lithium for the most part. That's not entirely true, it is possible to produce lithium in certain nuclear reactions, but it is easier to "burn" lithium in nuclear reactions. Stars probably "burn" more lithium than they create, which is why it is thought that most lithium is from big-bang nucleosynthesis.

    Beryllium:
    Beryllium is weirder yet. Beryllium is another element that gets skipped over in the normal process of fusion in stars. It is believed that most of the stable beryllium in the universe was originally created in the interstellar medium when cosmic rays induced fission in heavier elements found in interstellar gas and dust. So Beryllium is not star stuff (well, not created within stars anyway).

    Boron:
    Like beryllium, Boron is also created by by cosmic ray spallation and not by stellar nucleosynthesis. Boron is not created by stars.

    Carbon on up:
    Now we're talkin' star stuff (or decay products of former star stuff).

    [Edit: oh, and
    Sperm and eggs are made up of molecules, and those molecules are made of atoms. The atoms in the sperm and egg are still star stuff.* That's what the sources are saying.
    *(with the possible/arguable exceptions of the hydrogen atoms, and some of the other lighter atoms if any exist in the cell, that are discussed above.)]
     
    Last edited: Apr 10, 2013
  6. Apr 10, 2013 #5

    russ_watters

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    "Internet memes"?
     
  7. Apr 10, 2013 #6

    phinds

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    collinsmark, thank you for that excellent exposition.
     
  8. Apr 10, 2013 #7
    Thanks a lot for all the info guys. And thanks a lot collinsmark, that was a great read! I'm going to have to let that sink in for a bit. It looks like my first assumption was totally wrong.
     
  9. Apr 11, 2013 #8

    Astronuc

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    One can thank Carl Sagan for popularizing that notion - "we're made of star stuff".
     
  10. Apr 11, 2013 #9

    phyzguy

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    I think he was pre-dated by Joni Mitchell in her song "Woodstock" from the late '60's, which had the lyrics,

    " we are stardust, we are golden, .... billion year old carbon"
     
  11. Apr 11, 2013 #10
    Ancient Hindu texts supposedly have this too, but I was never able to confirm this.
     
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