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Oldest star HD 140283
Le lundi 21 janvier 2013 07:52:53 UTC+1, Yousuf Khan a écrit*:
On 20/01/2013 11:54 AM, Mike Dworetsky wrote: wrote: The star HD 140283 lies 190 light-years away from the Sun. It is 13.9 +/- .7 billion years old, whereas the Big Bang happenend 13.77 +/- s billion years ago. Where do you get your numbers for the star's age? This looks like a misquote. I think this might be where he got it from: "The team then exploited the fact that HD 140283 is in a phase of its life cycle in which it is exhausting the hydrogen at its core. In this phase, the star's slowly dimming luminosity is a highly sensitive indicator of its age, says Bond. His team calculates that the star is 13.9 billion years old, give or take 700 million years. Taking into account that experimental error, the age does not conflict with the age of the Universe, 13.77 billion years." Yes, thank you. Nearby star is almost as old as the Universe : Nature News & Comment http://www.nature.com/news/nearby-st...verse-1..12196 Statistically, what is the probability that HD 140283 is older than the BB? The error boundaries may overlap the age of the BB but no one thinks the star is possibly older than the BB. According to some hypothesis, the BB happened 13.77 +/- 0.059 Gyr ago. In order to appreciate the signification of such value, one could look at http://en.wikipedia.org/wiki/Age_of_the_universe. For instance, the age of the universe based on the best fit to WMAP data alone is 13.74 ± 0.11 Gyr. Using this last value, one could infer that HD 140283, aged 13.76 ± 0.11 Gyr, is a little older than the BB. Moreover, the first stellar generation must be older than HD 140283 itself. Yes. Yousuf Khan |
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Oldest star HD 140283
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Oldest star HD 140283
Le lundi 21 janvier 2013 16:13:30 UTC+1, Yousuf Khan a écrit*:
On 21/01/2013 9:00 AM, wrote: According to some hypothesis, the BB happened 13.77 +/- 0.059 Gyr ago. In order to appreciate the signification of such value, one could look at http://en.wikipedia.org/wiki/Age_of_the_universe. For instance, the age of the universe based on the best fit to WMAP data alone is 13.74 ± 0.11 Gyr. Using this last value, one could infer that HD 140283, aged 13.76 ± 0..11 Gyr, is a little older than the BB. Moreover, the first stellar generation must be older than HD 140283 itself. Where do you get HD 140283, aged 13.76 ± 0.11 Gyr? The article is saying 13.9 ± 0.7 Gyr. Sorry, my mistake! Anyways, even if it is 13.76 ± 0.11, just so long as the error bars fall within the BB, it's fine. If the error bars fall completely (i.e. both the top & bottom) outside the error bars for the Big Bang, then there might be something to talk about. I have to agree with you! Back about 20 years ago, they were estimating that some stars were maybe 20 billion years old, but the BB was already known to be only around 13.7 billion years by then. In all cases, it was simply that we didn't know stellar aging details well enough back then to make smaller error bars for them. Yousuf Khan |
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Oldest star HD 140283
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#16
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Oldest star HD 140283
wrote:
Le lundi 21 janvier 2013 09:26:40 UTC+1, Mike Dworetsky a écrit : wrote: Le dimanche 20 janvier 2013 17:54:26 UTC+1, Mike Dworetsky a écrit : wrote: The star HD 140283 lies 190 light-years away from the Sun. It is 13.9 +/- .7 billion years old, whereas the Big Bang happenend 13.77 +/- s billion years ago. Where do you get your numbers for the star's age? This looks like a misquote. According to the 2013 AAS abstract by Howard Bond et al http://adsabs.harvard.edu/abs/2013AAS...22144308B the age and its formal error due only to parallax uncertainty is 13.30 ± 0.30 Gyr. They say there are larger uncertainties from stellar parameters and chemical composition that are larger than 0.30 Gyr, though the abstract does not quote what these add up to, though they say "considerably larger". Statistically, what is the probability that HD 140283 is older than the BB? The error boundaries may overlap the age of the BB but no one thinks the star is possibly older than the BB. Mike Dworetsky Thank you. I read in the abstract that "Within the errors, the age of HD 140283 is slightly less than the age of the Universe, 13.76 ± 0.11 Gyr, based on the microwave background and Hubble constant." The BB happened 13.77 +/- 0.059 Gyr ago. Not sure why your figure differs from Bond et al. But our Galaxy must be older than HD 140283, thus older than the BB! Oh no, that isn't necessarily true at all! Our galaxy was (and is still being) formed from many mergers of smaller galaxies over a long period of time. In the Hubble Deep Fields all you see for very early epochs are small irregular objects, few if any spiral galaxies at the earlier stages. HD140283 could have come from the very early stages of star formation in one such fragment, and that could have merged into the forming Galaxy at any time. Not so long ago, many people thougt that our Earth was alone in the Universe. Not everyone, though. But all were agreed that detecting Earth-like planets would be very difficult, and only with the latest technology and space probes like Kepler has it become possible to look for them and find them. Now, it is presumed that billions of Earth-like planets are present in our galaxy. It's estimated/extrapolated from what we have already discovered, rather than presumed. Why wouldn't very many HD140283-like stars exist in our galaxy? And why wouldn't some of them be still older than HD140283? Of course there ought to be quite a few really old stars like this, but detecting them and measuring them accurately enough to determine absolute luminosity and hence age is very difficult, because most are far away and typically in the galactic halo. And yes, some could be even older, the quest continues. However, I can make a reasonably confident prediction that we will not find any stars that are verifiably older than the Big Bang. Finding stars formed a few hundred million years later than that is a useful confirmation of the Big Bang model. -- Mike Dworetsky (Remove pants sp*mbl*ck to reply) |
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Oldest star HD 140283
In article ,
Yousuf Khan writes: http://www.nature.com/news/nearby-st...iverse-1.12196 This seems to be full of errors. The actual AAS abstract is at http://adsabs.harvard.edu/abs/2013AAS...22144308B The age it gives is 13.3+/-0.3 Gyr, but the error bar is only from statistical uncertainty in the distance. The text says systematic errors are much larger than this. I haven't searched, but sometimes people put complete copies of their posters online. -- 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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