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Habitable zone

  1. Jul 20, 2014 #1
    I'm a physiologist, not in anyway well-versed in physics beyond what I took as a pre-medical student. Forgive any lapses in proper vocabulary or wording of my inquiries.

    I have a question about the habitable zone theory. Not so much this: http://en.wikipedia.org/wiki/Circumstellar_habitable_zone in terms of an individual star and satellite but moreso about the galaxy in general. What do you think of the galactic "habitable zone" theory that postulates life can really only exist in a narrow band of the galaxy. As wikipedia says, "the galactic habitable zone is the region of a galaxy in which life is most likely to develop [...] For the Milky Way this region is commonly believed to be an annulus with an outer radius of about 10 kiloparsecs and an inner radius close to the Galactic Center, both of which lack hard boundaries."

    The reason I am asking is because I am writer of science fiction, and while I'm not qualified to write really hard sci-fi, I'd rather not create alien planets in regions of the galaxy that even amateur cosmologists will read about and promptly throw my writing into the trash.
     
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  3. Jul 20, 2014 #2

    Student100

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    The whole Galaxy habitability zone is easy to take out of context. It doesn't suggest that life can only form in certain areas, but that complex life should be more common in certain locations within the galaxy.

    http://arxiv.org/pdf/astro-ph/0612316v1.pdf
     
  4. Jul 20, 2014 #3

    mathman

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    I can understand an inner boundary, beause of the black hole at the center. However, where did the 10 kiloparsec outer boundary come from?
     
  5. Jul 20, 2014 #4

    Student100

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    SN explosions due to high rates of star formation in the spiral arms, and I guess disturbing of a systems Oort Cloud which just doesn't sound very convincing.

    Then there is this http://onlinelibrary.wiley.com/doi/10.1029/2004GL021890/abstract
     
    Last edited: Jul 20, 2014
  6. Jul 20, 2014 #5

    marcus

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    The solar system is roughly 10 kpc from center, as I recall. that would be a bit over 30,000 lightyears.
    This source http://en.wikipedia.org/wiki/Galactic_Center says 8.3 kpc (or about 27,000 ly).

    I wouldn't worry. It is not as well-defined a concept as the circumstellar hab zone.

    What you want is stars and planets formed out of clouds that were enriched with heavier elements, not just H and He. But there are surely some of those out beyond 10 kPc
     
    Last edited: Jul 20, 2014
  7. Jul 21, 2014 #6

    Chalnoth

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    My guess would be it's all about metal abundance. You need a significant abundance of heavy elements for life to form, and that's only going to happen in regions where there are enough supernovae to form and disperse the heavy elements throughout the region.
     
  8. Jul 21, 2014 #7

    Student100

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    I thought there would be higher amounts of heavy elements found in the spiral arms?
     
  9. Jul 21, 2014 #8

    Matterwave

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    The spiral arms, being where the galaxy is most dense (the spirals are actually density fluctuations after all) are thus a center place for where new and active star formation forms. I've read that it's not desirable to live in the spiral arms themselves because of all this star formation, and therefore star death, which will lead to supernovae.

    Of course it's also not good to be in the halo because those are all old stars with very low metalicity. The central bulge is filled with too many stars apparently. So the guess is to look in the disc of the galaxy, between the spiral arms, not too close to the enter. (realistically speaking, even our exo planet search is centered on such a pathetically small neighborhood of our sun that such considerations are basically moot.)

    But really the whole galactic habitable zone theory is quite speculative. Even moreso than the stellar habitable zone theory which is itself already speculative. With only one sample point so far, it's pretty hard, actually impossible, to draw any hard conclusions.
     
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