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  #1  
Old May 16th 18, 12:22 PM posted to sci.astro.research
Steve Willner
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Posts: 1,127
Default First stars

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/UCAp...xmiV95A0ChueYg
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
Cambridge, MA 02138 USA
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  #2  
Old May 18th 18, 07:50 PM posted to sci.astro.research
Bringfried Stecklum
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Posts: 2
Default First stars

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/UCAp...xmiV95A0ChueYg
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

  #3  
Old May 19th 18, 09:07 AM posted to sci.astro.research
jacobnavia
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Posts: 94
Default First stars

Le 18/05/2018 Ã* 20:50, Bringfried Stecklum a écritÂ*:
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/UCAp...xmiV95A0ChueYg
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?

  #4  
Old May 19th 18, 10:08 AM posted to sci.astro.research
Richard D. Saam
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Posts: 223
Default First stars

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/UCAp...xmiV95A0ChueYg
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
  #5  
Old May 19th 18, 10:09 AM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Posts: 225
Default First stars

In article , jacobnavia
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.
  #6  
Old May 20th 18, 07:39 AM posted to sci.astro.research
jacobnavia
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Posts: 94
Default First stars

Le 19/05/2018 Ã* 11:09, Phillip Helbig (undress to reply) a écritÂ*:
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?

  #7  
Old May 20th 18, 07:40 AM posted to sci.astro.research
jacobnavia
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Posts: 94
Default First stars

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?

  #8  
Old May 20th 18, 09:05 PM posted to sci.astro.research
Jonathan Thornburg [remove -animal to reply][_3_]
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Posts: 132
Default First stars

jacobnavia 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]"
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"

  #9  
Old May 21st 18, 01:49 PM posted to sci.astro.research
jacobnavia
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Posts: 94
Default First stars

Le 19/05/2018 Ã* 11:09, Phillip Helbig (undress to reply) a écritÂ*:
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.
  #10  
Old May 21st 18, 01:50 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Posts: 225
Default First stars

In article , jacobnavia
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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