A Second Ladder to the Stars: Testing the Hubble Tension with Old Stellar Populations
Prof. Peter Garnavich
Department of Physics and Astronomy
University of Notre Dame
The Hubble constant estimated from Cepheid variables calibrating the luminosity of Type Ia supernovae is in tension with the Hubble constant derived from the cosmic microwave background (CMB) measurements. While this may imply physics beyond the standard model, the tension could be the result of unknown systematic errors in the Cepheid distance ladder. Cepheids are young massive stars found only in star-forming galaxies where dust and metal abundance variations can be important. We have developed a distance ladder that calibrates Hubble flow supernovae using Surface Brightness Fluctuations (SBF) and Tip of the Red Giant Branch (TRGB) methods that are independent of young stellar populations. Preliminary results from this new old-population ladder will be discussed.