Are the oldest stars too old for a Hubble constant of 0.73?
In plain words
The universe cannot be younger than its oldest stars. A faster expansion rate implies a younger universe, so precise ages of the oldest stars test which Hubble constant is right.
Precise statement
In flat LCDM the age is $t0 = 13.8\,\mathrm{Gyr}$ for $h = 0.674, \Omega_m = 0.315$ and about $12.9\,\mathrm{Gyr}$ for $h = 0.73, \Omega_m = 0.3$, while the oldest globular clusters, metal-poor stars and white dwarfs give ages near $13.3\text{ to }13.6\,\mathrm{Gyr}$ plus a formation delay of order $0.2\,\mathrm{Gyr}$. Determine whether these ages exceed the age allowed for $h = 0.73$ at more than $3\sigma$, with distance, reddening, alpha-element and stellar-physics systematics below $0.3\,\mathrm{Gyr}$. Cimatti and Moresco (2023, arXiv:2302.07899) obtained $h < 0.706$ from the most accurate ages.
What would settle it
Globular-cluster ages from Gaia distances and JWST photometry with full stellar-model error budgets, cross-checked with white-dwarf cooling ages.
Related problems
- Special case of What causes the Hubble tension?