The age of the universe

A minimum age of the universe can be estimated directly by determining the age of the oldest objects in our Galaxy. These objects are the metal-poor stars in the halo of the Milky Way. Recent work on nucleochronology finds that the oldest stars are 15.2 +/- 3.7 Gyr old. White dwarf cooling curves have found a minimum age for the oldest stars of 8 Gyr. Currently, the best estimate for the age of the oldest stars is based upon the absolute magnitude of the main sequence turn-off in globular clusters. The oldest globular clusters are 11.5 +/- 1.3 Gyr, implying a minimum age of the universe of t(universe) greater than or equal to 9.5 Gyr (95% confidence level). (C) 1998 Elsevier Science B.V. All rights reserved.