Testing White Dwarf Age Estimates Using Wide Double White Dwarf Binaries from Gaia EDR3

White dwarf (WD) stars evolve simply and predictably, making them reliable age indicators. However, self-consistent validation of the methods for determining WD total ages has yet to be widely performed. This work uses 1565 wide (>100 au) WD+WD binaries and 24 new triples containing at least two WDs to test the accuracy and validity of WD total age determinations. For these 1589 wide double WD binaries and triples, we derive the total age of each WD using photometric data from all-sky surveys, in conjunction with Gaia parallaxes and current hydrogen atmosphere WD models. Ignoring the initial-to-final mass relation and considering only WD cooling ages, we find that roughly 21%-36% of the more massive WDs in a system have a shorter cooling age. Since more massive WDs should be born as more massive main-sequence stars, we interpret this unphysical disagreement as evidence of prior mergers or the presence of an unresolved companion, suggesting that roughly 21%-36% of wide WD+WD binaries were once triples. Among the 423 wide WD+WD pairs that pass high-fidelity cuts, we find that 25% total age uncertainties are generally appropriate for WDs with masses >0.63 M (circle dot) and temperatures <12,000 K and provide suggested inflation factors for age uncertainties for higher-mass WDs. Overall, WDs return reliable stellar ages, but we detail cases where the total ages are least reliable, especially for WDs M (circle dot).

Automated summary

This study uses a sample of wide double WD binaries and triples to test the accuracy and validity of WD total age determinations. The results show that a significant portion of the more massive WDs have shorter cooling ages, suggesting prior mergers or the presence of unresolved companions. Reliable stellar ages are generally returned by WDs, with some exceptions for least reliable total ages, especially for higher mass WDs.