• First stars

    From Steve Willner@21:1/5 to All on Wed May 16 13:22:47 2018
    A recent _Nature_ article
    http://adsabs.harvard.edu/abs/2018Natur.555...67B
    shows evidence that the first stars appeared by z=20, about 180 Myr
    after the Big Bang. This is a preliminary result and still needs
    confirmation, but it's quite intriguing. Unfortunately there does
    not appear to be a free-access preprint of the article, but one of
    the authors will be giving the CfA Colloquium this Thursday at 4 PM
    EDT (UT-4). Colloquia are usually live-streamed; link at https://www.cfa.harvard.edu/colloquia
    or
    https://www.youtube.com/channel/UCApHNlZLkxmiV95A0ChueYg
    The latter link shows past colloquia but won't show the live stream
    (if at all) until just a minute or two before the talk starts.

    --
    Help keep our newsgroup healthy; please don't feed the trolls.
    Steve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA

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  • From Bringfried Stecklum@21:1/5 to Steve Willner on Fri May 18 19:50:17 2018
    On 16.05.2018 13:22, Steve Willner wrote:
    A recent _Nature_ article
    http://adsabs.harvard.edu/abs/2018Natur.555...67B
    shows evidence that the first stars appeared by z=20, about 180 Myr
    after the Big Bang. This is a preliminary result and still needs confirmation, but it's quite intriguing. Unfortunately there does
    not appear to be a free-access preprint of the article, but one of
    the authors will be giving the CfA Colloquium this Thursday at 4 PM
    EDT (UT-4). Colloquia are usually live-streamed; link at https://www.cfa.harvard.edu/colloquia
    or
    https://www.youtube.com/channel/UCApHNlZLkxmiV95A0ChueYg
    The latter link shows past colloquia but won't show the live stream
    (if at all) until just a minute or two before the talk starts.

    It looks the confirmation arrived quicker than thought. See ESO PR "The
    onset of star formation 250 million years after the Big Bang"

    https://www.eso.org/public/news/eso1815/

    which also provides a link to the paper.

    --
    Dr. Bringfried Stecklum
    Thüringer Landessternwarte
    Sternwarte 5
    07778 Tautenburg, Germany
    Phone: +49-36427-863-54
    FAX: +49-36427-863-29

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  • From jacobnavia@21:1/5 to All on Sat May 19 09:07:47 2018
    Le 18/05/2018 à 20:50, Bringfried Stecklum a écrit :
    On 16.05.2018 13:22, Steve Willner wrote:
    A recent _Nature_ article
    http://adsabs.harvard.edu/abs/2018Natur.555...67B
    shows evidence that the first stars appeared by z=20, about 180 Myr
    after the Big Bang. This is a preliminary result and still needs
    confirmation, but it's quite intriguing. Unfortunately there does
    not appear to be a free-access preprint of the article, but one of
    the authors will be giving the CfA Colloquium this Thursday at 4 PM
    EDT (UT-4). Colloquia are usually live-streamed; link at
    https://www.cfa.harvard.edu/colloquia
    or
    https://www.youtube.com/channel/UCApHNlZLkxmiV95A0ChueYg
    The latter link shows past colloquia but won't show the live stream
    (if at all) until just a minute or two before the talk starts.

    It looks the confirmation arrived quicker than thought. See ESO PR "The
    onset of star formation 250 million years after the Big Bang"

    https://www.eso.org/public/news/eso1815/

    which also provides a link to the paper.


    That's z=17. Looks nice z=17, with now an incredible bright QSO (quasar)
    with 20 Billion (!) solar masses and so bright that its light arrives
    directly to us, no gravitational lensing required, imagine. It is the
    most brilliant object detected so far by humans.

    https://arxiv.org/pdf/1805.04317.pdf

    The star mentioned above has oxygen, what implies at least several
    generations of stars to produce it, and then exploding and dispersing
    the oxygen into space so that it slowly condenses into anew stars...

    All that at z=17!

    Now this thing of 20 billion solar masses at the same epoch...

    20 Billion / 0.25 Gyears gives 80 solar masses swallowed by that hole
    since the "big bang", on average.

    But the stars needed to feed that hole must be born, and then swallowed.

    If it is swallowing gas, the process is much more inefficient since gas
    heats up... and stops the process.

    I suppose that at z=100 with CMB temperatures over 270K star formtion is
    not really possible isn't it?

    Let's assume that at 135K (z = 50) star formation could begin.
    That is 50 Million years after the "bang".

    That leaves us with only 200 million years to build that QSO. That means
    100 stars per year in average, one each 52 hours...

    That is possible, will argue many people. I do not think so.

    jacob

    P.S. The light from the quasar should be affected y this "star rain", at
    least it should oscillate when a new star is swallowed. Do we see that?

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  • From Richard D. Saam@21:1/5 to Bringfried Stecklum on Sat May 19 11:08:46 2018
    On 5/18/18 1:50 PM, Bringfried Stecklum wrote:
    On 16.05.2018 13:22, Steve Willner wrote:
    A recent _Nature_ article
    http://adsabs.harvard.edu/abs/2018Natur.555...67B
    shows evidence that the first stars appeared by z=20, about 180 Myr
    after the Big Bang. This is a preliminary result and still needs
    confirmation, but it's quite intriguing. Unfortunately there does
    not appear to be a free-access preprint of the article, but one of
    the authors will be giving the CfA Colloquium this Thursday at 4 PM
    EDT (UT-4). Colloquia are usually live-streamed; link at
    https://www.cfa.harvard.edu/colloquia
    or
    https://www.youtube.com/channel/UCApHNlZLkxmiV95A0ChueYg
    The latter link shows past colloquia but won't show the live stream
    (if at all) until just a minute or two before the talk starts.

    It looks the confirmation arrived quicker than thought. See ESO PR "The
    onset of star formation 250 million years after the Big Bang"

    https://www.eso.org/public/news/eso1815/

    which also provides a link to the paper.

    It is noted that Alan Rogers reports a dip in 21 cm absorption
    that ended at 250 million years.
    https://www.youtube.com/watch?v=yOq8I9b2SYI

    Richard D Saam

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  • From Phillip Helbig (undress to reply)@21:1/5 to jacob@jacob.remcomp.fr on Sat May 19 11:09:41 2018
    In article <pdnfql$b5u$1@dont-email.me>, jacobnavia
    <jacob@jacob.remcomp.fr> writes:

    Le 18/05/2018 20:50, Bringfried Stecklum a écrit :
    On 16.05.2018 13:22, Steve Willner wrote:
    A recent _Nature_ article
    http://adsabs.harvard.edu/abs/2018Natur.555...67B
    shows evidence that the first stars appeared by z=20, about 180 Myr
    after the Big Bang.

    It looks the confirmation arrived quicker than thought. See ESO PR "The onset of star formation 250 million years after the Big Bang"

    https://www.eso.org/public/news/eso1815/

    which also provides a link to the paper.

    That's z=17. Looks nice z=17, with now an incredible bright QSO (quasar)
    with 20 Billion (!) solar masses and so bright that its light arrives directly to us, no gravitational lensing required, imagine. It is the
    most brilliant object detected so far by humans.

    https://arxiv.org/pdf/1805.04317.pdf

    The star mentioned above has oxygen, what implies at least several generations of stars to produce it,

    Why? One generation will produce oxygen.

    and then exploding and dispersing
    the oxygen into space so that it slowly condenses into anew stars...

    Stars big enough to form appreciable oxygen quickly will explode anyway,
    so this is not an additional hurdle.

    All that at z=17!

    Keep in mind that the redshift, especially at high redshift, is a highly non-linear function of age. There is much less difference between z=17
    and z=12 than between z=0 and z=5.

    20 Billion / 0.25 Gyears gives 80 solar masses swallowed by that hole
    since the "big bang", on average.

    80 per year. But remember, the universe was denser back then, by a
    factor of (1+17)^3.

    But the stars needed to feed that hole must be born, and then swallowed.

    It doesn't have to be stars.

    If it is swallowing gas, the process is much more inefficient since gas
    heats up... and stops the process.

    It doesn't have to be gas. Maybe primordial black holes coalesced.

    I suppose that at z=100 with CMB temperatures over 270K star formtion is
    not really possible isn't it?

    Let's assume that at 135K (z = 50) star formation could begin.
    That is 50 Million years after the "bang".

    That leaves us with only 200 million years to build that QSO. That means
    100 stars per year in average, one each 52 hours...

    Again, it doesn't have to be stars. Also, several smaller black holes
    could have merged. Calculate (1+17)^3. Almost 6000. A very different environment.

    P.S. The light from the quasar should be affected y this "star rain", at least it should oscillate when a new star is swallowed. Do we see that?

    Again, you are assuming a specific model, based on essentially no
    information.

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  • From jacobnavia@21:1/5 to All on Sun May 20 07:40:07 2018
    Le 19/05/2018 à 11:09, Phillip Helbig (undress to reply) a écrit :
    Again, you are assuming a specific model, based on essentially no information.

    I am assuming that a quasar can be fed only by
    1) gas
    2) stars

    Gas is not possible (heats up and stops the process) so it must be whole stars...

    What else?

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  • From jacobnavia@21:1/5 to All on Sun May 20 07:39:37 2018
    Le 19/05/2018 à 11:09, Phillip Helbig (undress to reply) a écrit :
    Maybe primordial black holes coalesced.

    This hasn't been observed. Primordial black holes are very hypothetical
    and micro lensing observations rule them out as you said when discussing
    with Mr Oldershaw...

    Strange, now you think that they exist. Do you have any observations
    that point to those primordial black holes?

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  • From Jonathan Thornburg [remove -animal@21:1/5 to jacobnavia on Sun May 20 21:05:37 2018
    jacobnavia <jacob@jacob.remcomp.fr> wrote:
    See ESO PR "The
    onset of star formation 250 million years after the Big Bang"

    https://www.eso.org/public/news/eso1815/

    which also provides a link to the paper.

    This press release refers to

    Hashimoto et al,
    "The onset of star formation 250 million years after the Big Bang"
    https://arxiv.org/abs/1805.05966
    (open-access)
    published as
    Nature 557, 392-395
    https://www.nature.com/articles/s41586-018-0117-z
    (paywalled)

    This paper states

    # We detect an emission line of doubly ionized oxygen at a redshift of
    # 9.1096 +/- 0.0006, with an uncertainty of one standard deviation. This
    # precisely determined redshift indicates that the red rest-frame optical
    # colour arises from a dominant stellar component that formed about
    # 250 million years after the Big Bang, corresponding to a redshift of
    # about 15.

    That's z=17. Looks nice z=17, with now an incredible bright QSO (quasar)
    with 20 Billion (!) solar masses and so bright that its light arrives directly to us, no gravitational lensing required, imagine. It is the
    most brilliant object detected so far by humans.

    On the contrary, Hashimoto et al are observing a gravitationally lensed
    galaxy (the lensing increases it's apparent brightness by about a factor
    of 10, they say), not a QSO. They observe the galaxy at redshift z=9.1,
    and they infer from the galaxy's color that it contains stars which
    formed at a redshift of about z=15.

    https://arxiv.org/pdf/1805.04317.pdf

    *This* paper (1805.04317) describes an object at redshift z=4.75, not
    redshift z=17. (The paper does refer to "z=17", but that's a *magnitude*
    (log of brightness in a certain wavelength range), not a redshift. You
    can tell this because the paper says "magnitude z=17".)

    The star mentioned above has oxygen, what implies at least several generations of stars to produce it, and then exploding and dispersing
    the oxygen into space so that it slowly condenses into anew stars...

    As Phillip Helbig noted elsewhere in this thread, the first generation
    of stars could certainly have synthesized oxygen. See, for example
    https://en.wikipedia.org/wiki/CNO_cycle
    https://en.wikipedia.org/wiki/Alpha_process
    (The first figure in
    https://en.wikipedia.org/wiki/Nucleosynthesis
    shows "Exploding massive stars" as the main origin of oxygen; offhand
    I'm not sure if that's correct. Certainly non-explosive nucleosynthesis
    can also yield oxygen.

    [Moderator's note: Presumably what is important is not which stars
    produce the most oxygen, but which stars deposit the most oxygen into
    the interstellar medium from which new stars form. If the star doesn't explode, most of the oxygen won't get out. -P.H.]

    --
    -- "Jonathan Thornburg [remove -animal to reply]" <jthorn@astro.indiana-zebra.edu>
    Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA
    currently visiting Max-Plack-Institute fuer Gravitationsphysik
    (Albert-Einstein-Institut), Potsdam-Golm, Germany
    "There was of course no way of knowing whether you were being watched
    at any given moment. How often, or on what system, the Thought Police
    plugged in on any individual wire was guesswork. It was even conceivable
    that they watched everybody all the time." -- George Orwell, "1984"

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  • From Phillip Helbig (undress to reply)@21:1/5 to jacob@jacob.remcomp.fr on Mon May 21 14:50:00 2018
    In article <pdq5hd$dvp$1@dont-email.me>, jacobnavia
    <jacob@jacob.remcomp.fr> writes:

    Le 19/05/2018 à 11:09, Phillip Helbig (undress to reply) a écrit:
    Maybe primordial black holes coalesced.

    This hasn't been observed.

    What did LIGO observe? Of course, it is hard to prove that a black hole
    is primordial. However, if its mass is such that no other known
    mechanism could form it, then this increases faith in the primordial
    idea.

    Primordial black holes are very hypothetical

    They are an idea which has been around for a long time. Yes,
    hypothetical, but not really "very".

    and micro lensing observations rule them out as you said when discussing
    with Mr Oldershaw...

    Microlensing observations rule out a significant proportion of the dark
    matter being in the form of black holes (primordial or otherwise) of
    about a solar mass, which is what Mr Oldershaw was claiming. However, I
    have also mentioned the paper by Bernard Carr and Swedish collaborators
    here, which shows that very small and very large primordial black holes
    are not ruled out, particularly if they don't have all the same mass.

    Strange, now you think that they exist.

    Not strange at all; see above. I don't think that they exist, but
    rather point out that this is an explanation which has not yet been
    ruled out.

    Do you have any observations
    that point to those primordial black holes?

    Not directly, but see LIGO. However, I was reasonably certain that
    extrasolar planets exist before the first one was discovered.

    Also, define "observation". In some sense, if other means of growth are
    ruled out, observation of a large black hole might be evidence of
    primordial black holes.

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  • From jacobnavia@21:1/5 to All on Mon May 21 14:49:47 2018
    Le 19/05/2018 à 11:09, Phillip Helbig (undress to reply) a écrit :
    The star mentioned above has oxygen, what implies at least several
    generations of stars to produce it,
    Why? One generation will produce oxygen.


    Yes, but when the star explodes that oxygen will be enormouly diluted in
    the surrounding gas...

    To make an oxygen signal visible 13 Gy away the concentration of oxyygen
    should be quite high.

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  • From Phillip Helbig (undress to reply)@21:1/5 to jacob@jacob.remcomp.fr on Tue May 22 12:10:12 2018
    In article <pdq4rt$9ck$1@dont-email.me>, jacobnavia
    <jacob@jacob.remcomp.fr> writes:

    Le 19/05/2018 =E0 11:09, Phillip Helbig (undress to reply) a =E9crit :
    The star mentioned above has oxygen, what implies at least several
    generations of stars to produce it,
    Why? One generation will produce oxygen.

    Yes, but when the star explodes that oxygen will be enormouly diluted in
    the surrounding gas...
    To make an oxygen signal visible 13 Gy away the concentration of oxyygen should be quite high.

    Are you just making this up or did you get it from somewhere? Note also
    that the first stars might have been VERY massive, producing
    correspondingly more oxygen (no, I am not just making this up).

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  • From Steve Willner@21:1/5 to jacobnavia on Wed May 23 21:54:45 2018
    In article <pdq4rt$9ck$1@dont-email.me>,
    jacobnavia <jacob@jacob.remcomp.fr> writes:
    To make an oxygen signal visible 13 Gy away the concentration of oxyygen should be quite high.

    What mass of (doubly ionized) oxygen did you derive? Concentration
    doesn't matter, of course, but presumably mass was what you meant.
    You'll have to assume a density, but 10^3 cm^-3 would be a reasonable
    guess. I'm surprised the authors didn't do this calculation, but
    maybe they considered the density too speculative.

    --
    Help keep our newsgroup healthy; please don't feed the trolls.
    Steve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA

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  • From jacob navia@21:1/5 to All on Tue May 29 17:22:44 2018
    [[Mod. note -- I apologise for the delay in processing this article,
    which was originally submitted on Thursday 2018-05-24. -- jt]]

    Le 20/05/2018 à 22:05, Jonathan Thornburg [remove -animal to reply] a écrit :
    https://arxiv.org/pdf/1805.04317.pdf
    *This* paper (1805.04317) describes an object at redshift z=4.75, not redshift z=17. (The paper does refer to "z=17", but that's a*magnitude*
    (log of brightness in a certain wavelength range), not a redshift. You
    can tell this because the paper says "magnitude z=17".)


    Mr Thonburg is right. I have misunderstood that article.

    I apologize for this error.

    jacob

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