Measurement of stellar age from uranium decay

R. Cayrel (), V. Hill, T. C. Beers, B. Barbuy, M. Spite, F. Spite, B. Plez, J. Andersen, P. Bonifacio, P. François, P. Molaro, B. Nordström and F. Primas
Additional contact information
R. Cayrel: Observatoire de Paris-Meudon, DASGAL
V. Hill: European Southern Observatory
T. C. Beers: Michigan State University
B. Barbuy: Universidade de São Paulo
M. Spite: Observatoire de Paris-Meudon, DASGAL
F. Spite: Observatoire de Paris-Meudon, DASGAL
B. Plez: GRAAL, Université Montpellier-2
J. Andersen: Observatoire de Paris-Meudon, DASGAL
P. Bonifacio: Osservatorio Astronomico di Trieste
P. François: European Southern Observatory, Casilla 19001
P. Molaro: Osservatorio Astronomico di Trieste
B. Nordström: University of Copenhagen, Astronomical Observatory
F. Primas: European Southern Observatory

Nature, 2001, vol. 409, issue 6821, 691-692

Abstract: Abstract The ages of the oldest stars in the Galaxy indicate when star formation began, and provide a minimum age for the Universe. Radioactive dating of meteoritic material1 and stars2 relies on comparing the present abundance ratios of radioactive and stable nuclear species to the theoretically predicted ratios of their production. The radioisotope 232Th (half-life 14 Gyr) has been used to date Galactic stars2,3,4, but it decays by only a factor of two over the lifetime of the Universe. 238U (half-life 4.5 Gyr) is in principle a more precise age indicator, but even its strongest spectral line, from singly ionized uranium at a wavelength of 385.957 nm, has previously not been detected in stars4,5,6,7. Here we report a measurement of this line in the very metal-poor star CS31082-0018, a star which is strongly overabundant in its heavy elements. The derived uranium abundance, log(U/H) = -13.7 ± 0.14 ± 0.12 yields an age of 12.5 ± 3 Gyr, though this is still model dependent. The observation of this cosmochronometer gives the most direct age determination of the Galaxy. Also, with improved theoretical and laboratory data, it will provide a highly precise lower limit to the age of the Universe.

Date: 2001
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DOI: 10.1038/35055507

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