Probing the Universe’s expansion and the origin of compact object binaries with multi-messenger astronomy

Abstract: The synergy between gravitational wave (GW) experiments, such as LIGO/Virgo, and optical surveys, such as the Dark Energy Survey (DES), is most prominent in the discovery of electromagnetic counterparts to GW events and the application of the standard siren method, which has already enabled several measurements of the Hubble Constant. Our DES follow-up observations of the first binary neutron star merger detected by LIGO/Virgo enabled the discovery of the first optical counterpart to a GW event and the first standard siren measuement, while also providing information about the origin of the binary. We have later extended the standard siren analysis to compact object binary merger events without electromagnetic counterparts using galaxy catalogs, for which I will present the latest results. These measurements are a promising tool to shed light on the Hubble constant tension in the coming years. In the last part of the talk, I will present some interesting possibilities for the formation of the most massive binary black hole mergers detected so far which are related to galaxies’ central black holes, in particular those in dwarf galaxies and Active Galactic Nuclei.