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Did the heaviest elements come from other galaxys

  1. May 12, 2012 #1
    did the heavier elements come from different galaxys? im a gcse student who is in a bit of a debate with my teacher :)
  2. jcsd
  3. May 12, 2012 #2
    oh and all i have got is that "Brian Cox said it once i think." i am going to need a little more than that :)
  4. May 12, 2012 #3
    No, most local galaxies are pretty much the same. Depending on where you draw the line for "heavier", elements like carbon and oxygen are produced by the normal fusion processes in stars while elements beyond iron are mainly produced in supernovae.

    Because of the great distances between galaxies, only high-speed "cosmic rays" reach us from outside the Milky Way, though the Milky Way itself probably formed by the merger of smaller galaxies.


  5. May 12, 2012 #4


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    Given that the universe is extremely big and atoms are extremely small, some of every element in our galaxy came from Andromeda. Probably some of every element in your body came from Andromeda. What is your question exactly?
  6. May 13, 2012 #5


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    Why would you think this?
  7. May 13, 2012 #6
    Basically, phyzguy's argument is "due to the sheer number of atoms in someone's body, there's a good chance some came from Andromeda."
  8. May 13, 2012 #7
    I would have thought that a possibility [not the small atoms part] because earth has been bombarded by stuff for millions and likely billions of years, and formed from gases floating around for many more billions, so it would seem something might have had time to travel here from Andromedia....

    Do we have reason to believe any supernova explosion remnants in Andromedia could not or would not likely have reached our galaxy??

    After reading somebdy found one of the RNA proteins in meteor debris, I'd not rule much of anything out!!
  9. May 13, 2012 #8


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    The sheer distance to Andromeda is a huge impediment to anything originating there other than light reaching us. I don't know if Andromeda has been closer to us in the past, but at 2.5 million light years I'm not sure if anything can reach us or not. On top of that, any particles thrown out from a supernova would have to battle against the interstellar gas found inside Andromeda AND retain enough speed to beat escape velocity of the galaxy itself. No small feat.
  10. May 13, 2012 #9


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    Except for a relatively small number of relativistic particles, I really really doubt that any matter has reached us from Andromeda. Given the small number of such particles and the difficulty of capturing them, it seems very unlikely that there are any significant number on Earth.
  11. May 14, 2012 #10


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    The heavier elements in our galaxy came from supernovae within our galaxy. And likewise for other galaxies.
  12. May 14, 2012 #11


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    My reasoning is as follows:

    (1) Galaxies are filled with hot, ionized gas, with temperatures in the keV range, A proton with a temperature of 1 keV has an average velocity of about 400 km/sec.

    (2) A galaxy like Andromeda has a mass on the order of 10^12 Msun. At a distance of 10 kpc, the escape velocity is about 900 km/sec. Further out, the escape velocity is lower.

    (3) Therefore, the Maxwellian tail of the hot gas has enough velocity to escape the galaxy. This is similar to the Earth's atmosphere where the particles in the tail of the Maxwellian distribution evaporate over time.

    (4) A particle moving at 900 km/sec will cross the 800 kpc separating the Milky Way from Andromeda in about 0.8 gigayears. While this is a long time, the galaxies have been associated for much longer than this.

    (5) In addition, we see a constant stream of cosmic rays arriving at the Earth, with energies as high as 10^21 eV. These particles are relativistic, hence travelling at basically the speed of light, so there is no doubt they will escape, and they will cross intergalactic distances much faster. These are known to consist of elements at least as high as iron. Some of them almost certainly come from other galaxies.

    Therefore there should be a steady stream of atoms arriving from Andromeda, and other galaxies as well. I'm sure it is a tiny fraction of the atoms associated with the Milky Way, but it is still a huge number of atoms. For those of you who disagree, are you saying that none of the perhaps 10^68 baryons in the Milky Way came from Andromeda? Or do you disagree with the analysis above?
  13. May 14, 2012 #12


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    The original post was asking about heavy elements. The number of those that escape the galaxy will be exponentially-damped, in addition to their low abundances.
  14. May 15, 2012 #13
    The heaviest elements come from supernovae, in any galaxy.

    Is the Milky Way static? I'm pretty sure it has merged with other galaxies in the past, taking in all of its elements, heavy or not.

    So if you are asking did ALL the heaviest elements come from another galaxy, then I would say NO! If on the other hand you are asking if some COULD have come from another galaxy, then I would say why the heck not!?!
  15. May 15, 2012 #14
    Your argument to that point is OK but can you complete the analysis to support your claim that:
    You also ask:
    I agree your analysis as far as it goes, am disagreeing with your understanding of the orginal question:
    It doesn't ask about tiny fractions, the implication I understood from the question was that someone was claiming that our galaxy could not produce heavy elements (or perhaps only in small quantities) and that they predominantly came from some other type of galaxy.
  16. May 15, 2012 #15

    D H

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    Your analysis was for protons. The question is about the heaviest elements, not protons. The tiny amount of uranium atoms in a hot interstellar gas cloud at a temperature of 107K have a mean velocity of 33 km/sec. This means that essentially none of the uranium atoms in the Earth came from Andromeda. Instead, they all came from supernovae that occurred within the Milky Way or in galaxies that subsequently merged into the Milky Way.
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