Program: GN-2018B-Q-303

Title:Microlensing black holes and their masses from Gaia
PI:André-Nicolas Chené
Co-I(s): K. Rybicki, A. Hamanowicz, P. Mroz, S.T. Hodgkin, K. Kruszynska, L. Wyrzykowski, M. Gromadzki

Abstract

Our Milky Way is probably full of stellar-mass black holes, but so far only about 50 are known, and all are in X-ray binaries. Gravitational microlensing is the only tool capable of detecting single black holes, which are not interacting with anything. However, despite of more than 15,000 microlensing events found to date, we are not able to tell which ones are due to black holes. Combination of photometry from the ground and astrometric time-series from Gaia will yield mass measurements for the longest lasting events, but without the lens and source distances, the degeneracy between massive stars and black holes still remains. We propose to conduct Standard ToO GMOS observations of selected microlensing events from the Galactic plane outside of the bulge, for which Gaia will provide astrometric data and which are good candidates for lensing black holes, in order to constrain the spectral type of their sources and any blends.