Australian astronomers on Sunday said they had found a star 13.6 billion years old, making it the most ancient star ever seen. The star was formed just a couple of hundred million years after the Big Bang that brought the Universe into being, they believe. Previous contenders for the title of oldest star are around 13.2 billion years old—two objects described by European and US teams respectively in 2007 and 2013. Read more at: http://phys.org/news/2014-02-oldest-star-iron-fingerprint.html#jCp
Interesting. However, I believe the title is not accurate. What was observed was the lowest-level metallicity of any previous observation. I've commented previously recently that the lower the metallicity the older the star. With one with this low of a metallicity, it is believed to be a 'Population III' star. http://en.wikipedia.org/wiki/Metallicity However, as of the date of that wikipedia article (2010) it was believed that no Population III stars existed in our aged region of the Universe, and one needed to look to more distant regions for such early-formation stars. So this poses another conundrum -- why does it still exist, when it was supposed to have gone supernova billions of years ago? I suspect that claiming a fairly accurate 'age' based solely on metallicity (as the authors of your quoted article do) is not valid. There could be other reasons for a very low metallicity, such as a star forming in a region relatively unperturbed by Population III and Population II supernovae, then drifting into its present location. So yes, quite interesting to have a low-metallicity star in our neighborhood. But no, not proof of it being the oldest star along the lines of the age they propose.
it is believed to be a Pop II star not III. and the reason it hasn't gone supernova is that it isn't big enough.
"The findings, which are published this week in the journal Nature, provide a glimpse of what the activity in the very early universe may have looked like, and point to much more diverse properties among the very first population of stars." So I'm not convinced it is the oldest simply because it has the lowest metallicity. There are several others that are quite low, and it is suggested that this star's 'progenitor' (assuming there was only 1 nearby supernova giving the weak iron signature in the daughter star) might have had a much 'weaker' infusion of iron, which makes the dating essentially impossible.
I'm not sure if you are right or wrong Walter...A discovery has been made.....Further studies no doubt will reveal more exacting data. I found the article fascinating and decided to post as I do with other articles.
I'm not quibbling that they found something new. I'm quibbling with the title "oldest star". Lowest metallicity, yes; oldest star, only maybe. Here's more from the article: "But the new second-generation star may change scientists' understanding of just how active the very first generation of stars was. Because the newly identified star has both very low iron and relatively high carbon content, Frebel envisions an alternative scenario: that this star arose from a low-energy, first-generation star whose explosion expelled the contents of its outer layers, but was not strong enough to release chemicals such as iron from its inner layers. The resulting gas cloud—high in carbon, and low in iron—eventually coalesced to form SMSS J031300.36-670839.3." So if this is the case, how can they claim it is older than the other low-metallicity stars, in particular the ones with similar iron content, but quite old. If they envision this one was formed from an iron-deficit explosion (hence greater carbon), then it could well be younger than the other ones with similar iron content, but not quite as low in iron-metallicity as this one. This quotation seems to contradict the claim that the low iron metallicity makes it the oldest -- when they also argue it has low iron-metallicity because of an iron-deficient supernova (high in carbon). In other words, if it had been enriched by a normal supernova instead of an iron-deficient supernova, then it should be younger, not older. That's what I'm quibbling about. I believe "they" used the title to promote their research and discovery, which is not a good idea as it essentially is making a fake claim on otherwise interesting work. (I note that the term 'oldest star' is in quotes in the PhysOrg review article, so this appears to be coming from a reviewer, not the authors of the work.)) Additionally, the entire dating methodology leaves a great deal of uncertainty, certainly not being able to claim a date to 3 significant digits (13.6). There is much more work that needs to be done in this area. A feeble enrichment because of greater distance from a supernova does not an older star make. Subsequent Note: The online article is somewhat different: "NATURE | LETTER A single low-energy, iron-poor supernova as the source of metals in the star SMSS J031300.36−670839.3 The element abundance ratios of four low-mass stars with extremely low metallicities (abundances of elements heavier than helium) indicate that the gas out of which the stars formed was enriched in each case by at most a few—and potentially only one—low-energy supernova1, 2, 3, 4. Such supernovae yield large quantities of light elements such as carbon but very little iron. The dominance of low-energy supernovae seems surprising, because it had been expected that the first stars were extremely massive, and that they disintegrated in pair-instability explosions that would rapidly enrich galaxies in iron5. What has remained unclear is the yield of iron from the first supernovae, because hitherto no star has been unambiguously interpreted as encapsulating the yield of a single supernova. Here we report the optical spectrum of SMSS J031300.36−670839.3, which shows no evidence of iron (with an upper limit of 10−7.1 times solar abundance). Based on a comparison of its abundance pattern with those of models, we conclude that the star was seeded with material from a single supernova with an original mass about 60 times that of the Sun (and that the supernova left behind a black hole). Taken together with the four previously mentioned low-metallicity stars, we conclude that low-energy supernovae were common in the early Universe, and that such supernovae yielded light-element enrichment with insignificant iron. Reduced stellar feedback both chemically and mechanically from low-energy supernovae would have enabled first-generation stars to form over an extended period. We speculate that such stars may perhaps have had an important role in the epoch of cosmic reionization and the chemical evolution of early galaxies." http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12990.html So, the summary article claims iron, but the original article says no iron with an upper limit. Quite a bit of difference, and sloppy reading of the original article by the summarizing article you posted.
Wouldn't a star that forms from hydrogen and helium, which are very abundant in the universe, also show no iron?
Actually this star is a Population II star. It does contain some metals. Population III stars would be almost impossible to find anywhere but at extreme look-back times. The reason is because they would form as truly massive stars and have a short life-span. Finding one will probably have to wait on the next generation of super telescopes. Perhaps with the Webb but that is an iffy prospect. Resolving a single star well enough to get a decent spectrograph at z = 12 or so is quite a tall order. There is also a slight, very slight chance a Pop III star could form nearer by IF (a big if) somehow there were some large enough cloud of truly pristine gas that has somehow managed to survive intact and isolated from all galactic groups and clusters.
