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Question about star evolution

  1. Jun 4, 2015 #1
    I was thinking about this the other day, and I was curious about what future stars will contain for their cores.

    If I understand correctly, the first generation stars in the early universe didn't contain (or contained significantly less) metals. As stars evolved, they contained more metals (or maybe they produced more metals?).

    Will future stars become more metallic as they evolve, creating new metals, or maybe even new elements?

    Part 2 to this question is: is this why scientists state that X matter may not exist, and that it may eventually be created through star evolution?

    I hope my understanding isn't off, but if it is, please let me know :)

    Cheers!
     
  2. jcsd
  3. Jun 4, 2015 #2

    Chronos

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    More recently formed stars are known to have greater metallicity than stars formed earlier in the universe. Unsurprisingly dying stars significantly contribute to metallicity of the interstellar media, the birthing crate of new stars. We do not expect to discover hitherto unknown elements being formed by stars,so the periodic table is safe from upstart elements based on our knowledge of nuclear physics. We can only deduce what metals may exist in stellar cores, our spectrometers can only see the elements that exist in the atmosphere of stars and any intervening media along our line of sight.
     
  4. Jun 4, 2015 #3
    Over a very long time scale and very gradually, stars have been increasing the total amount of heavier elements present in the interstellar medium,
    It's reasonable to assume this is going to continue into the very distant future with new generations of stars (and associated planets) containing more of these elements at the start of their existence..
    The interstellar medium at present contains a significant amount of gas and dust, mostly the lighter element such as carbon and oxygen.
    Primordial hydrogen though is still by far the greatest part of it.
    The heaviest elements such as Uranium are rare and thought to be only produced in supernovas which are themselves rare,
    As far as I know Uranium is the heaviest of all naturally occurring elements, although a few heavier ones, notably Plutonium have been synthesised (using special nuclear reactors designed for this purpose.)
     
    Last edited: Jun 4, 2015
  5. Jun 4, 2015 #4

    Chalnoth

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    To add a little to this: the reason why we don't expect to discover unknown elements is that we have discovered the first nearly 120 elements. It's fundamentally impossible for there to be any unknown elements between those (because the number of protons determines the element). And the higher-mass elements only last for tiny fractions of a second before they decay into lighter elements, so these really heavy elements can't really be "discovered" in stars per se, because they're gone the moment they're created.
     
  6. Jun 4, 2015 #5
    Thank you for the clarification. That was going to be my next question :P
     
  7. Jun 4, 2015 #6

    e.bar.goum

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    Not quite true, at least historically. Back when we thought that the island of stability was going to (a) be easier to reach and (b) there would be stable superheavy isotopes, it was certainly thought that super-heavy isotopes would be produced in supernova explosions. So, one of the ways that nuclear physicists attempted to find new elements was to look for in mineral samples on earth from e.g. deep sea sediment crusts to see supernova remnants.

    Further, by nuclear physics standards, the superheavy elements that we have created in labs actually live for a reasonably long time (compared to, say, 8Be). There are still models that predict that there will be genuinely stable superheavy isotopes, and still papers that talk about finding them in nature. E.g. http://nrv.jinr.ru/pdf_file/aip_2012_1491.pdf (The same physicist also once suggested that the best place to look for super-heavies on earth would be after a nuclear explosion. I'm not sure how he proposed to look.)
     
  8. Jun 5, 2015 #7

    Chalnoth

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    Eh, doubt it. The average half-life of these elements drops off pretty rapidly, and the relatively stable isotopes become fewer and further between. Reading up on it a bit, it looks like the "island of stability" for superheavy isotopes is expected to have a maximal half life of around a few hours. I seriously doubt that's long enough for astrophysical observations, especially as the production rate for any very heavy elements is already going to be very low:
    http://en.wikipedia.org/wiki/Island_of_stability

    My understanding is that a lot of the hopes of stable superheavy elements were dashed by the discovery of new decay modes that become available for heavier elements.
     
  9. Jun 5, 2015 #8

    Chronos

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    The stability plateau idea for elements above 220 has largely been abandoned as I recall.
     
  10. Jun 5, 2015 #9

    e.bar.goum

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    Hence "historic" in my above post. The concept of "island of stability" is certainly still in play (the shell model still applies, after all), but no-one really thinks there will be isotopes with very long half-lives. The correct phrase might be "the island of (relative) stability". There is very little agreement in the literature however, for how long lived the region of stability will be. Seconds, hours, perhaps? There is also little agreement for where it is either. Superheavy element research is excellent for pinning down models of nuclear structure.

    Amusingly, the current method for super-heavy element detection (via chains of alpha decay) is actually very insensitive to long-lived superheavy elements - if the half-life is much more than a ms or so, you can't detect it, as the next beam pulse will have long ago wiped you out.


    Yeah, these days very few people think they're possible to see in nature (with notable exceptions, see the above proceedings).

    It's not so much the discovery of new decay modes (they all pretty much alpha-decay), but more sophistication in models of nuclear structure. But they themselves aren't very constrained. Better reaction models also tell us a lot about cross sections - not big! Quasi-fission is a real issue.

    ETA: It's worth reiterating that for a nuclear physicist, an hour long half-life may as well be stable. This is why we talk about "region of stability" even though there is unlikely to be any truly stable (as in "infinite half-life") superheavies.
     
  11. Jun 5, 2015 #10
    So it seems like there may be a possibility of discovering a new element, but it's very slim and/or may not be anything usable due to decay?

    Are future generation stars expected to be similar to the stars that exist today, or is there any speculation/theories that predict some sort of evolution?
     
  12. Jun 5, 2015 #11
    Other than that the total amount of relatively common fusion products such as oxygen in the universe will very slowly increase there isn't any reason to suppose dramatic differences in the future generations of stars.
    Existing stellar nuclear processes are well understood in theory and are consistent with observations, and there is no basis to assume any fundamental change to these.
     
    Last edited: Jun 5, 2015
  13. Jun 5, 2015 #12

    SteamKing

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    When astronomers talk about the "metallicity" of stars or their "metal" content, they are actually referring to the presence of any element which has an atomic mass greater than hydrogen or helium, not necessarily to substances with which we are familiar as metals existing in a terrestrial environment.

    http://en.wikipedia.org/wiki/Metallicity
     
  14. Jun 5, 2015 #13
    But by no means monotonously.
    Polonium 209 - half-life 125 years
    polonium 210 - 138 days
    polonium 211 - 516 ms
    polonium 212 - 299 ns...​
    astatine 210 - 8,1 h
    astatine 211 - 7,2 h
    astatine 212 - 310 ms
    astatine 213 - 125 ns...​
    radon 211 - 14,6 h
    radon 212 - 24 min
    radon 213 - 19 ms
    radon 214 - 270 ns...​
    francium 212 - 20 min
    francium 213 - 34 s
    francium 214 - 5 ms
    francium 215 - 86 ns...​
    radium 213 - 2,7 min
    radium 214 - 2,4 s
    radium 215 - 1,5 ms
    radium 216 - 182 ns...​
    actinium 214 - 8,2 s
    actinium 215 - 170 ms
    actinium 216 - 0,44 ms
    actinium 217 - 69 ns...​
    thorium 215 - 1,2 s
    thorium 216 - 27 ms
    thorium 217 - 0,24 ms
    thorium 218 - 109 ns...​
    protactinium 216 - 105 ms
    protactinium 217 - 3,5 ms
    protactinium 218 - 0,11 ms
    protactinium 219 - 53 ns...​
    "Quite obviously" all elements with 92 or more protons or 220 or more nucleons are extremely unstable with half-life a small fraction of a second...

     
  15. Jun 5, 2015 #14
    Thank you for that clarification and link. As you guessed, I did think that it was in reference to actual metals.
     
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