Institute for Advanced Study/Princeton University Joint Astrophysics Colloquium

Our understanding of the dynamics of our Local Group of galaxies has changed dramatically over the past few years owing to significant advancements in astrometry and our theoretical understanding of galaxy structure. I will provide an overview of key contributions by the Hubble Space Telescope to this evolving picture. In particular, I will highlight the impact of the HSTPROMO team’s proper motion measurements of key players in the Local Group, such as the most massive satellites of the Milky Way (the Large and Small Magellanic Clouds), the first direct proper motion measurement of M31 and an implied new orbital history for M33. These results have met with controversy, challenging preconceived notions of the orbital dynamics of key components of the Local Group. They also make concrete predictions and have profound implications for our analysis of upcoming high-precision astrometric data from e.g., Gaia, LSST and JWST.