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The star, HE 1523-0901 - which is located in our galaxy - was found to be 13.2 billion years old by a team using the European Southern Observatory’s Very Large Telescope (VLT) to measure not one, but six radioactive ‘cosmic clocks’.
 | Measurement of the radioactive decay of 'cosmic clocks'
can give clues as to the age of distant stars |
Anna Frebel, of the MacDonal Observatory in the US, and leader of the study said: “Surprisingly, it is very hard to pin down the age of a star. 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.”
The technique is similar to the carbon-14 dating method that has been so successful in archaeology, whereby items can be dated according the abundance of radioactively decayed carbon isotopes. In astronomy however, the technique must be applied to vastly longer timescales - meaning that to remain useful the radioactive cosmic ‘clock’ used must not decay too quickly leaving enough of it to allow accurate measurement.
The key to the team’s success was the combination of six different measurements of age dating involving both thorium and uranium in combination with 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” said Frebel.
The universe is thought to be 13.7 billion years old, suggesting that the star was formed very early in the life of our own galaxy.
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