Undergraduate Physics Seminar: "Gravitational-Wave Background Measurements of Cosmological Expansion using Data from LIGO's 4th Observing Run," Vanessa Zhang

It is well-known that the Universe is expanding, but the value of its current expansion rate—the Hubble constant, H0—is contested. In this presentation, I focus on the “stochastic siren”, a new method to measure H0 using gravitational waves (GWs). GWs are generated by astrophysical events such as binary black hole (BBH) mergers, some of which are detected by the LIGO-Virgo-Kagra (LVK) Collaboration. The stochastic siren considers not only these detected events, but also ones that the LVK cannot see: unresolved events composing the GW background (GWB). We hence consider two sources of data: the foreground of resolved GW signals from BBH mergers and upper limits on unresolved signals obtained from the GWB search. These data are influenced by the BBHs’ redshifts and masses, as well as the underlying cosmological description that includes H0. By using models to parametrize these quantities, we can extract an estimate of H0. I will introduce the general method and preliminary results from performing this analysis on the most recent, fourth observation run of the LVK Collaboration. 

Join via Zoom: https://illinois.zoom.us/j/84466699377?pwd=PoAMbQGYd24NS2AuwwvYgh1i3Iuvfg.1