The Cosmic Clock (IMAGE) ESO Caption From left: Recent cosmological studies show that the Big Bang occurred 13.7 billion years ago. The metal-poor star HE 1523 formed in our Milky Way galaxy soon afterward, cosmologically speaking: 13.2 billion years ago. The primitive star contained the radioactive heavy elements uranium and thorium, and the amounts of those elements decay over time, each according to its own half-life. Today, astronomer Anna Frebel of the the University of Texas at Austin McDonald Observatory and her colleagues have deduced the star's age based on the amounts of radioactive elements it contains compared to certain other "anchor" elements, specifically europium, osmium and iridium. The study of the star's chemical make-up was made using the UVES spectrograph on the Kueyen Telescope, part of ESO's Very Large Telescope, at Paranal, in Chile. Credit (c) ESO Usage Restrictions All ESO photographs are Copyright (c) ESO. ESO press photos are clearly marked as ESO pictures. Regarding permission to reproduce ESO images, editors of newspapers and bona-fide science magazines and journals (including popular science magazines) may use these pictures without any reproduction charge, but reference must be always be given to ESO, e.g. by the line License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.