Please contact Beth Demkowski, demkowsk@umich.edu for Zoom link.

The current discrepancy between early- and late-Universe measurements of the Hubble constant (H0) highlights the need for additional independent and precise probes. Gravitationally lensed quasars can provide one such probe. Quasars are galaxies with an active galactic nuclei (AGN), usually a black hole, whose light output varies over time. We can measure the light output over time from each image of the lensed quasar. The different travel time for the light from each image means that the variations show up at different times for each image. Measuring the time delay between pairs of images and combining it with a model of the lens allows one to infer H0.

Over the past decade a number of improvements in both the data quality and modeling techniques have allowed the measurement of H_0 from time-delays to start to fulfill its promise of being competitive with other traditional methods such as the cosmic distance ladder.

I will present the current state of the H0 measurement from gravitationally lensed quasars and discuss future prospects.