The age of the galactic globular cluster system

A careful assessment of current uncertainties in stellar physics (opacities, nuclear reaction rates, equation of state effects, diffusion, rotation, and mass loss), in the chemistry of globular cluster (GC) stars, and in the cluster distance scale, suggests that the most metal-poor (presumably the oldest) of the Galaxy's GCs have ages near 15 Gyr. Ages below 12 Gyr or above 20 Gyr appear to be highly unlikely. If these approximate to 2 sigma limits are increased by similar to 1 Gyr to account for the formation time of the globulars, and if standard Friedmann cosmologies with the cosmological constant set to zero are assumed, then the GC constraint on the present age of the Universe (t(0) greater than or equal to 13 Gyr) implies that the Hubble constant H-0 less than or equal to 51 km s(-1) Mpc(-1) if the density parameter Omega = 1 or less than or equal to 62 km s(-1) Mpc(-1) if Omega = 0.3.