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There's an old-timer in the neighborhood, and it's got a story to tell. A new study of a relatively nearby old star shows that it’s almost as old as the big bang itself.
The star HD 140283 lies about 190 light-years away in the constellation Libra. Astronomers have long known that it's ancient, because it contains mostly hydrogen and helium—which were present at the dawn of the universe—and few of the heavy elements that were forged later in stellar furnaces.
With the Hubble Space Telescope, researchers have now pinned down the distance to HD 140283, which allowed them to determine how bright the star is. Along with the chemical composition of the star, the newly derived stellar properties allowed for a new age estimate.
The study of HD 140283, in the Astrophysical Journal Letters [Howard E. Bond et al., HD 140283: A Star in the Solar Neighborhood That Formed Shortly after the Big Bang], found that the star is 14.46 billion years old. But the entire universe, as you may have heard, is only 13.77 billion years old. The two age estimates aren't actually in conflict, because there’s always some uncertainty. The full age estimate is thus 14.46 billion years plus or minus 800 million years. Put your money on the minus.
—John Matson
[The above text is a transcript of this podcast.]
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2 Comments
Add CommentJust a cotton-pickin' minute. I thought, bigger the star, shorter the fuse. And where are any companions that would have coalesced at the same time? Surely we should be looking for others- this one won't be an orphan? High velocity sub-giant it says. What gave it the speed boost? Am I barking up the wrong Hertzsprung-Russell diagram? Please enlighten an simple old questor.
Reply | Report Abuse | Link to thisGood catch! I had read through this necessarily brief podcast transcript and didn't find anything particularly interesting, but as you point out, the linked "Astrophysical Journal Letters" abstract states:
Reply | Report Abuse | Link to this"HD 140283 is an extremely metal-deficient and high-velocity subgiant in the solar neighborhood, having a location in the Hertzsprung-Russell diagram where absolute magnitude is most sensitive to stellar age. Because it is bright, nearby, unreddened, and has a well-determined chemical composition, this star avoids most of the issues involved in age determinations for globular clusters..."
My interest was piqued by the statement that is was "high-velocity" yet its light was "unreddened", as I wondered how its velocity had been determined except through spectral analysis. I did find a freely accessible draft version of the research report at
http://hubblesite.org/pubinfo/pdf/2013/08/pdf.pdf
I'm not an astronomer, so there may be some very telling information in the report that I've missed. However, I find that this star is not a new a new discovery, so I presume the news is a new age estimate. In section 2, "The Extreme Halo Subgiant HD 140283", the star is described as an "A-type subdwarf". I don't find much about them, but the Sun is designated as a yellow dwarf star based on its spectral class. I guess that this subdwarf is likely less massive than the Sun - perhaps accounting for its apparently very reliably estimated longevity.
As for its high velocity, being a proximal object in the stellar halo, its tangental velocity relative to the Earth may be very high since it is essentially independently orbiting the Milky Way, apparently at a relatively low radial distance. I guess it's near the Earth now, but won't be much longer...
Most halo stars are thought to have been gravitationally captured. It's possible that its sibling stars are also orbiting the MW, perhaps at greater distances, or they may be halo objects orbiting another galaxy!
Again, I'm not an astronomer so may have misinterpreted something, but this is a more interesting story than the brief podcast could describe - thanks again for pointing it out!