Siyang (Sean) Li

Siyang Li studies the present expansion rate of our universe, parameterized by the Hubble constant (H0), to investigate the Hubble Tension. The Hubble Tension is a sizable discrepancy between measurements of H0 using information from the early and late universe and suggests a need to identify significantly underestimated uncertainties, or revise the canonical model of our universe; either class of solutions would have profound impacts on the field as they would require shifts in our understanding of these respective phenomena at the level of several standard deviations. One powerful way to probe systematic uncertainties in the Hubble Tension is to develop and use independent ways to measure H0. As a PhD student at Johns Hopkins, Li worked on refining tools that can be used to measure H0, including the tip of the red giant branch and J-region Asymptotic Giant Branch (JAGB), to investigate systematic uncertainties and develop independent routes to measure H0. In particular, the JAGB is a new tool that can be used to independently measure H0; however, recent studies have shown evidence of intrinsic variations that still need to be investigated before they can be used to robustly crosscheck H0. As a Brinson Prize Fellow, Li will perform extensive characterizations of the stars used for the JAGB method using both ground- and space-based telescopes to investigate and improve this technique and probe the origins of the Hubble Tension.