Program: GS-2023A-DD-107

The population of the Milky Way includes a number of components that are challenging to observe, if not invisible...and yet measuring these populations is essential for a complete understanding of stellar evolution. Isolated stellar remnants, such as black holes, produce no accretion or gravitational wave signatures, but can be detected from the deflection in the light of a background star that their gravity produces as they pass in front. This microlensing signature can also be used to explore the population of low-mass stars and planets. Historically confined to the Galactic Bulge, the Gaia Mission was the first alert producing, time-domain survey to make it viable to search for these events across the whole galaxy. But they survey data cannot fully characterize the event with spectroscopy to determine the spectral type of the source star. This allows degeneracies in the microlensing model to be broken, enabling us to measure the mass of the lens. We request urgent spectroscopic observations of a high priority ongoing microlensing discovery from Gaia.