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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 |
#2
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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
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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
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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
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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
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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
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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
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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
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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
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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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