Stellar ages and their cosmological context

Stellar ages have traditionally been used to constrain cosmological models by setting lower limits to the age of the universe. We quickly review the basic cosmological concepts that underpin the derivation of a finite age, and the constraints given by the measure of cosmological parameters at a redshift z ∼ 1000. The most direct way of measuring stellar ages through the abundance of radioactive elements is shown to suffer from systematics in the evaluation of the production ratios, to the extent that the constrains are less stringent that previously thought. The discrepancy between the ages of the oldest stars and the cosmologically inferred age of the universe may well be dominated by systematc effects in the predicted evolution of low-mass stars.