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The universe's oldest known star: Like a needle in a haystack


“It was very much a needle-in-a-haystack situation.”
 
Dr. Stefan Keller was “pleasantly surprised” when his team discovered what is believed to be the oldest known star in the universe.
 
 
Discovered through the lens of the ANU’s SkyMapper telescope (a device that uses 268m pixels to capture an area 29 times the size of the full moon per minute) at the Siding Spring observatory in New South Wales, the star was identified by the researchers during the course of working on a detailed map of the cosmos in the southern sky.
 
Dr Keller, a researcher from the Australian National University’s Research School of Astronomy and Astrophysics, had been working with researchers from Australia, Germany, the United Kingdom, and the United States over a period of 11 years. The group’s findings were recently published in the journal Nature.
 
Star search
 
The star, which was given the designation SMSS J031300.36-670839.3, is estimated to be about 6,000 light-years away from our planet. To find it, the researchers had to sift through spectral data collected on the 60 million stars that SkyMapper managed to capture during its first year of operation.
 
By studying the chemical composition of the surface of a star, it is possible to gauge how old or young it is. Since the chemicals found on its surface are remnants of the star that came before it, and because more elements have been introduced into the universe throughout the passing of time, it is reasonable to assume that (a) younger stars have a greater assortment of elements on their surfaces, and (b) stars with fewer traces of chemicals – especially iron, one of the first "heavy" elements created – most likely formed much earlier in the universe’s history.
 
The researchers crossed out any stars that had spectra similar to our sun (whose surface is relatively chemical-rich) in order to zero in on the oldest stars in the selection. Then, they picked out the stars with very low chemical signatures and obtained high-resolution spectral data on them using the Magellan Telescopes, a powerful pair of telescopes in Chile.
 
The makings of a star
 
The researchers were able to conclude that SMSS J031300.36-670839.3 contained a relatively low level of iron – less than one-millionth of our sun’s, and about 60 times less than any other star.
 
“The telltale sign that the star is so ancient is the complete absence of any detectable level of iron in the spectrum of light emerging from the star,” explained Dr Keller, in an essay on The Conversation.
 
“We can use the iron abundance of a star as a qualitative “clock” telling us when the star was formed.”
 
Furthermore, the researchers examined the level of carbon in the star, and found that the element was about a thousand times more abundant there than iron. 
 
It is possible that the newly discovered star came from a first-generation star that exploded in such a way that it only fully released the elements present in its outer layers, and not the elements present in its inner layers (such as iron). As a result, a gas cloud with a high carbon level and low iron level may have led to the formation of SMSS J031300.36-670839.3.
 
These findings radically affect how scientists view the first generation of stars, in terms of their level of chemical activity.
 
“This star had a lower-than-expected explosion energy, and also lower than today's regular supernovae, which was really an unexpected finding,” said co-author Anna Frebel (http://phys.org/news/2014-02-oldest-star-iron-fingerprint.html), who hails from the Massachusetts Institute of Technology's Kavli Institute for Astrophysics and Space Research.
 
“That tells us that, to some extent, we have to go back to the drawing board, because there is more variety amongst this very first generation of stars than we have assumed so far." — TJD, GMA News
Tags: astronomy
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