[asa] Ancient Universe: 13.2 Billion Year Old Star Found

From: Rich Blinne <rich.blinne@gmail.com>
Date: Sun May 13 2007 - 09:11:57 EDT

A galactic fossil: Star is found to be 13.2 billion years
How old are the oldest stars" Using ESO's VLT, astronomers recently measured
the age of a star located in our Galaxy. The star, a real fossil, is found
to be 13.2 billion years old, not very far from the 13.7 billion years age
of the Universe. The star, HE 1523-0901, was clearly born at the dawn of
time. <http://physorg.tradepub.com/?pt=cat&page=_INTL> "Surprisingly, it
is very hard to pin down the age of a star", the lead author of the paper
reporting the results, Anna Frebel, explains. "This requires measuring very
precisely the abundance of the radioactive elements thorium or uranium, a
feat only the largest telescopes such as ESO's VLT can achieve."

This technique is analogous to the carbon-14 dating method that has been so
successful in archaeology over time spans of up to a few tens of thousands
of years. In astronomy, however, this technique must obviously be applied to
vastly longer timescales.

For the method to work well, the right choice of radioactive isotope is
critical. Unlike other, stable elements that formed at the same time, the
abundance of a radioactive (unstable) isotope decreases all the time. The
faster the decay, the less there will be left of the radioactive isotope
after a certain time, so the greater will be the abundance difference when
compared to a stable isotope, and the more accurate is the resulting age.

Yet, for the clock to remain useful, the radioactive element must not decay
too fast - there must still be enough left of it to allow an accurate
measurement, even after several billion years.

"Actual age measurements are restricted to the very rare objects that
display huge amounts of the radioactive elements thorium or uranium," says
Norbert Christlieb, co-author of the report.

Large amounts of these elements have been found in the star HE 1523-0901, an
old, relatively bright star that was discovered within the Hamburg/ESO
survey [1]. The star was then observed with UVES on the Very Large Telescope
(VLT) for a total of 7.5 hours.

A high quality spectrum was obtained that could never have been achieved
without the combination of the large collecting power Kueyen, one of the
individual 8.2-m Unit Telescopes of the VLT, and the extremely good
sensitivity of UVES in the ultraviolet spectral region, where the lines from
the elements are observed.

For the first time, the age dating involved both radioactive elements in
combination with the three other neutron-capture elements europium, osmium,
and iridium.

"Until now, it has not been possible to measure more than a single cosmic
clock for a star. Now, however, we have managed to make six measurements in
this one star"," says Frebel.

Ever since the star was born, these "clocks" have ticked away over the eons,
unaffected by the turbulent history of the Milky Way. They now read
13.2billion years.

The Universe being 13.7 billion years old, this star clearly formed very
early in the life of our own Galaxy, which must also formed very soon after
the Big Bang.

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Received on Sun May 13 09:12:19 2007

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