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

Understand

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.