Implications for the Hubble tension from the ages of the oldest astrophysical objects

TL;DR

This study uses ages of old astrophysical objects across redshifts to set an upper limit on the Hubble constant, challenging some local measurements and suggesting the need for new physics to resolve the Hubble tension.

Contribution

It provides a novel age-based constraint on H_0 using objects up to redshift 8, highlighting potential discrepancies with local measurements and implications for cosmological models.

Findings

Upper limit on H_0: <73.2 km/s/Mpc at 95% confidence

Discrepancy with local H_0 measurements, suggesting new physics may be needed

Supports the idea of modifications to ΛCDM to resolve the Hubble tension

Abstract

We use the ages of old astrophysical objects (OAO) in the redshift range $0 \lesssim z \lesssim 8$ as stringent tests of the late-time cosmic expansion history. Since the age of the Universe at any redshift is inversely proportional to $H_0$, requiring that the Universe be older than the oldest objects it contains at any redshift, provides an upper limit on $H_0$. Using a combination of galaxies imaged from the CANDELS program and various high-$z$ quasars, we construct an age-redshift diagram of $\gtrsim 100$ OAO up to $z \sim 8$. Assuming the $\Lambda$CDM model at late times, we find the 95\% confidence level upper limit $H_0<73.2\,{\rm km}/{\rm s}/{\rm Mpc}$, in slight disagreement with a host of local $H_0$ measurements. Taken at face value, and assuming that the OAO ages are reliable, this suggests that ultimately a combination of pre- and post-recombination ($z \lesssim 10$) new physics might be required to reconcile cosmic ages with early-time and local $H_0$ measurements. In the context of the Hubble tension, our results motivate the study of either combined global pre- and post-recombination modifications to $\Lambda$CDM, or local new physics which only affects the local $H_0$ measurements.