The Hubble Constant From Stellar Ages

Mathematics – Logic

Scientific paper

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Scientific paper

Globular star clusters are the oldest objects in the Universe for which reliable ages can be derived and, in view of their great age and because the Universe cannot be younger than its contents, they provide one of the most important of the few constraints that we have on cosmological models. In this review(Based largely on material contained in VandenBerg, D.A., Bolte, M., & Stetson, P.B. 1996, Ann.Rev.Astr.Ap.), 34, in press., it is argued that the most metal-poor (presumably the oldest) of the Galaxy's globular clusters (GCs) have ages near 15 Gyr --- just as most investigators of these systems have found since the early 1970's. A careful assessment of current uncertainties in stellar physics (opacities, nuclear reaction rates, equation of state effects, diffusion, rotation, mass loss), in the chemical composition of the member stars, and in the cluster distance scale suggests that ages below 12 Gyr or above 20 Gyr are highly unlikely. If these ≈ 2σ limits are increased by ~ 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 age of the Universe (t0 >= 13 Gyr) implies that the Hubble constant H0 <= 51 km s-1Mpc-1 if the density parameter Ω = 1 or <= 62 km s-1Mpc-1 if Ω = 0.3.

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