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#21
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An old galaxy at z=7.1
On 3/6/2015 8:59 AM, jacob navia wrote:
Le 04/03/2015 20:55, wlandsman a écrit : There are many possible clear and definitive tests but here's a simple one -- find any object that has an origin more than 13.8 billion years ago. .. .. .. If we take your argument further, if you see an object that is X years old with an universe thatis only Y years old (YX) that disproves BB theory too. The argument was not about disproving BB, the question was what result would (the words of Robert O's message lead us to think that there is a problem with our theoretical model of the early period of expansion?" So there could be other errors than the BB concept (like insufficiently taking into account discrete scale relativity, or other shortcomings. That would remain to be seen then!) ... The new MUSE instrument at ESO is also pretty incredible. It can see objects in the HDF South that Hubble did not see at all, AND taking their spectra! I think it will be that instrument that will bring the big bang to explode. Actually I don't see how _that_ would disprove it.. But I do hope the instrument will teach us more about the 96% (by mass) of physics that we don't yet understand! -- Jos |
#22
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An old galaxy at z=7.1
On Friday, March 6, 2015 at 10:20:01 AM UTC-5, Phillip Helbig (undress to reply) wrote:
In other words, if someone finds evidence that the universe is, say, 14.5 Gyr old, then there is no problem. (Of course, any new value would also have its own error bar.) If the error bars overlap, one would expect the values to converge as measurements become better. On the other hand, convincing evidence that the universe is, say, 20 Gy old would require more than just adjusting the estimate. ----------------------------------------------------------- What you describe is how the plastic model-building version of science works. Theories of principle can make definitive predictions that are non-adjustable. That form of science has a lot more integrity, in my opinion. [Mod. note: like it or not, the BB model is based on observation of the universe we actually inhabit, and its parameters are not derived from first principles. Please, let's take both that and the obvious responses pointing out failed non-adjustable predictions of 'competitor' models as read, and try to find something that's both original and interesting to say. -- mjh] |
#23
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An old galaxy at z=7.1
On Friday, March 6, 2015 at 2:59:54 AM UTC-5, jacob navia wrote:
Le 04/03/2015 20:55, wlandsman a écrit : Take a pair of binoculars, and look into the constellation of Libra. There, you can see HD 140283, that lies 190.1 light-years away. Its age was before estimated to 16 billion years. Now, NASA has brought that down into 14.5 billion. Further tweaking by the astronomers will surely bring that star into the desired range :-) French astronomers have already brought the age down. Crevey et al. (2015, http://adsabs.harvard.edu/abs/2015A%26A...575A..26C ) now estimate the age as 13.7 +/- 0.7 Gyr if there is no reddening, and 12.2 +/- 0.6 Gyr for a very modest (but plausible) reddening (A_V = 0.1). (This work is done by stellar astronomers, not by cosmologists.) We are seeing now a dusty galaxy that must have formed in only 150 million years can you imagine? It is hard for me to image a 150 million year old galaxy that is *not* dusty. Try googling the phrase "dusty starburst". |
#24
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An old galaxy at z=7.1
Le 06/03/2015 17:14, Jos Bergervoet a écrit :
There are many possible clear and definitive tests but here's a simple one -- find any object that has an origin more than 13.8 billion years ago. .. .. .. I note that you snipped the object older than the universe that can be seen with a pair of binoculars... The latest estimate (14.5 billion years +/- 0.8 Gy) is still older than the universe as the big bang would have it. In the *best* case this star is 13.7 billion years, so it must have formed IMMEDIATELY after the supposed bang!!! And this is an otherwise run of the mill star, that is in our nearest neighborhood; just 190.1 light years away. What a coincidence isn't it? [Mod. note: 1-sigma error bars are not a definitive range. If this measurement were right (and it's already been updated, see wlandsman's post) then we could say with ~99.9% confidence that the age is 12.1 Gyr, hardly a serious problem for the BB model. Posters are encouraged to apply *basic* statistics to any numbers they want to introduce to the discussion -- mjh] |
#25
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An old galaxy at z=7.1
Le 06/03/2015 16:20, Phillip Helbig (undress to reply) a écrit :
NASA has not "brought that down". Rather, estimates are improved with time. That's why people continue to study objects which have been studied before. OK, but this is STILL older than the universe! 14.5 is bigger than 13.7 as far as I understood maths. I am always accused of not bringing more "numbers", more "facts"! OK. Here iks a number FOURTEEN POINT FIVE that is bigger than 13.7. OK, the error bars. Plus/minus 0.8 billion years, so in the BEST case, this star was formed instataneusly after the bang since 14.5 - 0.8 -- 13.7 Gy In the *best* case since in all other cases this star is older as the universe... But this fact will be "explained" away and we will go on as before. |
#26
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An old galaxy at z=7.1
In article ,
jacob navia writes: http://www.eso.org/public/archives/r...8/eso1508a.pdf This is an interesting paper, but because it's in _Nature_, not all the information is given. In particular, it looks to me as though the uncertainties on the physical quantities are underestimated, and I don't see how the authors derive the expected equivalent width for the C III] line. (It isn't in the reference cited.) A dust temperature as low as 35 K also strikes me as unlikely; the CMBR temperature is 23 K, after all. None of this changes the basic and valuable result that there must be _some_ dust in the galaxy, and in fact more of the galaxy's luminosity comes out in the rest-frame FIR than in the UV. There is a vast literature on processes that create and destroy dust. Despite that, there are still large uncertainties about the dust life cycle because the creation and destruction rates depend critically on local environmental conditions and on the exact dust composition. Also, dust _masses_ are notoriously hard to measure. The age estimate for the stellar population of A1689-zD1 is 80 Myr, and I see no reason why dust amounting to about 2% of the stellar mass (by the authors' estimate; rather less by my estimate) cannot have been created in that time. As to A1689-zD1 contradicting the Big Bang, our present knowledge of early galaxy formation and the progress of reionization is highly uncertain. Better understanding of the early Universe is indeed a prime objective of JWST. That said, a _rough_ picture of the timing as presently understood is that the first galaxies might have formed between redshift 11 and 20, substantial reionization (say 1% of the volume ionized) begins around redshift 8 or lower, and reionization is nearly finished (99% of the volume ionized) no later than redshift 5.5. Further data will refine or perhaps change these numbers, but so far as I know, there are no existing data inconsistent with them. As others have written, the new data on this galaxy are consistent with these epochs. Finally, what would it take to throw out the present Big Bang picture? I can think of two obvious things: 1) an object at any redshift older than the calculated age of the Universe at that redshift, or 2) a microwave background temperature at any redshift differing from (1+z)*2.7 K. (wlandsman mentioned #1.) Less obvious but still sufficient would be failure to find any single set of cosmological parameters consistent with all data. Of course such contradicting observations would have to be confirmed and have low uncertainties and systematic errors, not be simply 1- or 2-sigma deviations or observations where the meaning is unclear. A couple of decades ago, globular cluster ages were thought to constitute such a problem, but _Hipparcos_ data showed the cluster distances were wrong and therefore the ages were overestimated. As I wrote, at the moment there's no problem despite considerable data. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#27
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An old galaxy at z=7.1
On Sat, 07 Mar 15, Steve Willner wrote:
Finally, what would it take to throw out the present Big Bang picture? ... 2) a microwave background temperature at any redshift differing from (1+z)*2.7 K. I wonder what you'd think of this paper: "The Temperature Of The z=8.4 Intergalactic Medium" -- http://arxiv.org/abs/1503.00045 . They measure the "spin temperature" of the IGM at z=8.4 and are hard-pressed to reach as high as 10K. I don't understand much of the paper, though. Eric |
#28
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An old galaxy at z=7.1
On Saturday, March 7, 2015 at 3:45:50 AM UTC-5, jacob navia wrote:
I note that you snipped the object older than the universe that can be seen with a pair of binoculars... Sigh. The name of this star is HD 140283 -- it is the nearest halo star to the Sun with V = 7.2 and a distance of 190 light years in the constellation of Lyrae. The French astronomers I quoted obtained interferometry for this star and greatly reduced the uncertainties in its age determination. Their best age determination is 13.7 +/- 0.7 Gyr if there is no reddening, and 12.2 +/- 0.6 Gyr for a very modest (but plausible) reddening (A_V = 0.1). The latest estimate (14.5 billion years +/- 0.8 Gy) is still older than the universe as the big bang would have it. No. The latest estimate is from the French paper. Please don't quote an obsolete press release but use the improved results ( http://adsabs.harvard.edu/abs/2015A%26A...575A..26C ). And as the moderator noted, please don't ignore the 1 sigma error bars. I find it remarkable that cosmoslogists are able to estimate the age of the universe but studying tiny temperature fluctuations in the microwave background. And this age turns out to be entirely consistent with the ages of the oldest stars and of high redshift galaxies. --Wayne |
#29
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An old galaxy at z=7.1
In article , wlandsman
writes: I find it remarkable that cosmoslogists are able to estimate the age of the universe but studying tiny temperature fluctuations in the microwave background. And this age turns out to be entirely consistent with the ages of the oldest stars and of high redshift galaxies. Indeed. The CMB gives us lambda, Omega, and H, and hence the age. The values for lambda, Omega, and H are also essentially the same as those derived from other methods---several of them---without using the CMB at all. It is thus not just the one parameter---age---which agrees from several independent determinations, but the individual parameters used to calculate it as well. |
#30
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An old galaxy at z=7.1
Le 08/03/2015 09:38, wlandsman a écrit :
Their best age determination is 13.7 ± 0.7 Gyr if there is no reddening, and 12.2 ± 0.6 Gyr for a very modest (but plausible) reddening (A_V = 0.1). quote The adoption of one particular result for AV then becomes arbitrary. In this work we determine AV in the direction of the star along with F(bol) using a SED fitting method, described below. However, we also fix AV = 0.0 mag and discuss our results considering both possible scenarios end quote It is interesting that you do not take into account the precise wording of the authors of that paper. The reddening hasn't been observed by some observers, the star is very near (just 190 ly) so this reddening parameter looks highly suspicious to me, not "plausible" as you say. This is very dangerous for an unbiased analysis of the data that in astronomy can be very difficult to evaluate. The authors of that paper conclude the abstract with: quote Theoretical advances allowing us to impose the mixing-length parameter would greatly improve the redundancy between M, Yi, and age, while from an observational point of view, accurate determinations of extinction along with asteroseismic observations would provide critical information allowing us to overcome the current limitations in our results end quote They say that their accuracy can (and should) be improved! You wrote: quote Please don't quote an obsolete press release but use the improved results end quote The paper you cite is from December 2014. I just wasn't aware of that very new publication. As I said, I see that we have reached the point where the age of the star fits into the framework that many astronomers wish. But this is not a final analysis, as the authors themselves write in their abstract. To be continued! jacob |
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