Setting a cosmic clock with highly charged ions

The amount of Os-187 in meteorites resulting from beta decay of the long-li ved Re-187 nuclide (half-life 42 billion years in the neutral charge state) has been used as a measure of the time span of nucleosynthesis in our Milk ey Way galaxy. During the galactic evolution, however, the rhenium atoms, g enerated in the r-process, can be "astrated" several times into just origin ating stars, where they are stripped of most or all of their electrons. An experiment conducted at the ion storage ring ESR at Darmstadt established f or bare Re-187 ions a half-life of only 33 years, that is by more than nine orders of magnitude shorter than the corresponding half-life in the neutra l atomic charge state. Based on this amazing result, the half-life for any other charge state of Re-187 can be calculated and, accordingly the effecti ve lifetime of Re-187 during nucleosynthesis can be figured out in the fram ework of well-founded evolution models of our galaxy. That allows a re-cali bration of the rhenium "aeon clock" from which, tentatively a lower limit o f 12 billion years for the age of our galaxy was derived being, a fortiori, also a lower limit for the age of the universe. In connection with recent results for the Hubble constant this limit provides narrow constraints for actual cosmological models.