White-Dwarf Cooling Ages Inside Globular Clusters Compared With Turnoff Ages of the Same Systems

A globular cluster contains two independent clocks. The turnoff clock reads the nuclear lifetime of stars now leaving the main sequence; the white-dwarf clock reads how long the cluster's dead stars have been cooling. This study compares published values of both clocks in 4 clusters where deep Hubble photometry reaches the end of the cooling sequence. Averaged over the sample, the two clocks differ by 0.95 billion years. The largest tension is in 47 Tucanae, where the clocks differ by 1.85 billion years, a 2.4 standard deviation discrepancy on the published errors. Because both clocks date the same stellar population, a persistent offset of this size points to a shared ingredient — distance, composition, or cooling physics — rather than to cosmology, and any cosmological use of cluster ages must first absorb it. The comparison is computed from published values, not measured.