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Thread: Oldest Galaxy

  1. #1
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    Oldest Galaxy

    This can't be right? How can enough stars have formed to form an entire galaxy in 600 million years.
    Big Bang - Expansion - 'dark' period - ionization and still have enough time to form galaxies?
    http://www.space.com/30170-most-dist...iscovered.html

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    Quote Originally Posted by Rathkennamike View Post
    This can't be right? How can enough stars have formed to form an entire galaxy in 600 million years.
    Big Bang - Expansion - 'dark' period - ionization and still have enough time to form galaxies?
    http://www.space.com/30170-most-dist...iscovered.html
    Got it backwards. The galaxies apparently formed out of gas clouds, then stars formed in them. The current prevailing theory is that uneven distribution of dark matter drew them together.
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  3. #3
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    Here's a paper on the galaxy:

    http://arxiv.org/pdf/1507.02679v2.pdf

    Title: LYMAN-ALPHA EMISSION FROM A LUMINOUS z=8.68 GALAXY: IMPLICATIONS FOR GALAXIES AS TRACERS OF COSMIC REIONIZATION

    The indications are that it had heavy star formation, and quoting:

    Although uncertainties remain, the demographics and limited spectroscopic follow-up of this early population has been used to argue that star-forming galaxies played a significant role in completing the reionization of the intergalactic medium (IGM) by a redshift z ∼ 6
    So studying galaxies like this helps in teasing out the details of the reionization process.

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    Actually this has to be right because galaxies exist, Rathkennamike .
    A star the size of our Sun requires about 50 million years to mature from the beginning of the collapse to adulthood. - but that is formation from gas clouds inside a existing galaxy.
    The First Stars in the Universe has models predicting that the first stars appeared between 100 million and 250 million years after the big bang. 350 million years for this observation looks to me plenty of time for the stars to collect into galaxies.

  5. #5
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    Thanks for that timeline which goes some way to answer my question. However despite the timeline you give, the universe must have been very dense at that time for sufficient stars to form.
    But if we count from BB then if we see galaxies at 600my then the other processes I mention must have taken very little time.
    A related question is; is the existence of black hole essential for galaxy formation or do black holes only form in the centre of galaxies (Still open question)

  6. #6
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    Not only has there been plenty of time for stars to form, there has been enough for several generations of stars.
    The first can only have contained hydrogen, the only element in the Universe at that time.
    As the first stars aged and some exploded in supernovae, they seeded the Universe with heavier elements, up to Iron that formed in the verfy high heat and pressure in the core of a star that has exhausted all its hydrogen.
    Astronomers talk of three "Populations" of stars, by the relative quantities of heavier elements, that they call 'metals', in them.
    Someone else must explain how elements heavier than Iron were created.

    Oh, and RC, surely the stars didn't collect into galaxies, but matter collected into dust/gas clouds that gave rise to galaxies of stars?

    John

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    Quote Originally Posted by JohnD View Post
    The first can only have contained hydrogen, the only element in the Universe at that time....
    ...except for helium, which was also fairly prevalent at about 25%. The other light elements (deuterium, lithium) fused in the first few minutes were so scarce as to be nearly negligible.

    Stars can only fuse up to iron near the end of their life cycle, but when they go supernova, elements heavier than iron are fused.
    Everyone is entitled to his own opinion, but not his own facts.

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    Quote Originally Posted by Noclevername View Post
    Got it backwards. The galaxies apparently formed out of gas clouds, then stars formed in them. The current prevailing theory is that uneven distribution of dark matter drew them together.
    That sounds about right, according to hydrodynamic models anyway. A recent article in Nature had this to say:


    "The specifics of how galaxies form from, and are fuelled by, gas from the intergalactic medium remain uncertain. Hydrodynamic simulations suggest that ‘cold accretion flows’—relatively cool (temperatures of the order of 104 kelvin), unshocked gas streaming along filaments of the cosmic web into dark-matter halos—are important. These flows are thought to deposit gas and angular momentum into the circumgalactic medium, creating disk- or ring-like structures that eventually coalesce into galaxies that form at filamentary intersections...."
    Everyone is entitled to his own opinion, but not his own facts.

  9. #9
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    whatever happened to MACS1149-JD ? The wikipedia page on this galaxy cites a redshift of 9.6, which is bigger than the redshift for EGSY8p7

    https://en.wikipedia.org/wiki/MACS1149-JD

    There's also this article on space.com, where it is said that MACS1149-JD is "the earliest known confirmed galaxy"

    http://www.space.com/17671-farthest-...onal-lens.html

    "The earliest known confirmed galaxy has been discovered with the help of cosmic lenses ..."
    Last edited by iron4; 2015-Aug-14 at 05:15 PM.

  10. #10
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    MACS 1149-D, as far as I can tell, still has a redshift value which is modeled from multifilter intensity measurements, which is both a good bit less accurate than a spectroscopic value (which requires spectral lines strong strong for our equipment to detect) and has a nontrivial rate of dramatic failures (if the galaxy's energy distribution is not well fit by the models available; strong dust reddening is a common concern). The new z=8.7 report is special because it has a spectroscopic redshift from the Lyman-alpha emission line, so its redshift is much more secure.

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