Description:

One of the central open questions in cosmology is whether the standard ΛCDM model fully describes the evolution of the Universe, or whether new physics is required. A key test comes from measurements of the Hubble constant, H₀, the present-day expansion rate of the Universe. Direct, local determinations of H₀ based on Cepheids and Type Ia supernovae currently yield values that differ, at the 5–6σ level, from those inferred from observations of the cosmic microwave background. If this “Hubble tension” is real, it may point to physics beyond ΛCDM. In this talk, I will present recent results from the Chicago–Carnegie Hubble Program (CCHP), which aims to measure H₀ with unprecedented accuracy using multiple, independent distance indicators. Leveraging new James Webb Space Telescope NIRCam observations with four times the spatial resolution and an order-of-magnitude gain in sensitivity over HST, we have obtained improved distances to nearby galaxies using the tip of the red giant branch (TRGB), Cepheid variables, and the J-region asymptotic giant branch (JAGB) method. Together, these methods provide independent calibrations of Type Ia supernovae. These data are bringing us closer to resolving whether the Hubble tension is a measurement issue, or a window into new physics.

Wendy Freedman, Professor, University of Chicago

Host: Vicky Kalogera