16681

Observations of the orbits of stars around the supermassive black hole at the center of our Galaxy have brought us new and exciting insights into the physics and astrophysics of supermassive black holes. These observations have not only provided the best evidence so far for the existence of supermassive black holes comma but they have also advanced our understanding of star formation and stellar dynamics in this region. With a time baseline of over 25 years comma we can perform ever more powerful experiments comma the latest of which are measurements of the effect of General Relativity on the orbit of the star S0-2-S2. As astrometry becomes more precise comma the discovery of our Galaxy.s dark cusp of compact objects is now within reach. However comma there is a fundamental limitationdoublePoint the stability of the reference frame. We propose to observe the Galactic center with WFC3-IR in the next three cycles comma which when combined with Gaia data will create the most accurate reference frame to date. These measurements from 2022-2024 will (1) enable the detection of a dark cusp around the black hole (2) take advantage of the unique overlap in observations between HST comma Gaia (ending in 2024) comma JWST (beginning in 2022) comma and the ground to cross-calibrate instrumental systematic uncertainties to build on the legacy of astrometry with HST (3) use HST observations to double our yearly time baseline for monitoring the near-infrared activity of Sgr A* to determine the physical origins of its recent unprecedented increase in activity.