The discovery of the second highly r -process-enhanced , extremely metal-poor star , CS 31082-001 ( [ Fe/H ] = -2.9 ) has provided a powerful new tool for age determination , by virtue of the detection and measurement of the radioactive species uranium and thorium .
Because the half-life of ^ { 238 } U is one-third that of ^ { 232 } Th , the U-Th pair can , in principle , provide a far more precise cosmochronometer than the Th-Eu pair that has been used in previous investigations .
In the application of this chronometer , the age of ( the progenitor of ) CS 31082-001 can be regarded as the minimum age of the Galaxy , and hence of the universe .

One of the serious limitations of this approach , however , is that predictions of the production ratio of U and Th have not been made in the context of a realistic astrophysical model of the r -process .
We have endeavored to produce such a model , based on the “ neutrino winds ” that are expected to arise from the nascent neutron star of a core-collapse supernova .
In this model , the proto-neutron star mass and the ( asymptotic ) neutrino sphere radius are assumed to be 2.0 M _ { \odot } and 10 km , respectively .
Recent hydrodynamic studies indicate that there may exist difficulties in obtaining such a compact ( massive and/or small in radius ) remnant .
Nevertheless , we utilize this set of parameter choices since previous work suggests that the third r -process peak ( and thus U and Th ) is hardly reached when one adopts a less compact proto-neutron star in the framework of the neutrino-wind scenario .
The temperature and density histories of the material involved in the neutron-capture processes are obtained with the assumption of a steady flow of the neutrino-powered winds , with general relativistic effects taken into account .
The electron fraction is taken to be a free parameter , constant with time .
The r -process nucleosynthesis in these trajectories is calculated with a nuclear reaction network code including actinides up to Z = 100 .

The mass-integrated r -process yields , obtained by assuming a simple time evolution of the neutrino luminosity , are compared to the available spectroscopic elemental abundance data of CS 31082-001 .
As a result , the “ age ” of this star is determined to be 14.1 \pm 2.5 Gyr , in excellent agreement with lower limits on the age of the universe estimated by other dating techniques , as well as with other stellar radioactive age estimates .
Future measurements of Pt and Pb in this star , as well as expansion of searches for additional r -process-enhanced , metal-poor stars ( especially those in which both U and Th are measurable ) , are of special importance to constrain the current astrophysical models for the r -process .