Program: GN-2016A-DD-3

We propose to use the Doppler technique on time-resolved Gemini North/GMOS-N spectroscopy to infer the minimum mass of a compact object companion to a recently discovered extremely metal-poor star. Data already acquired suggests that the object is a stellar mass black hole, but the sparse radial velocity sampling currently available does not exclude the possibility that the companion is a white dwarf or neutron star. If the compact object is confirmed to be a black hole, it would be the closest known black hole to the Sun. The visible extremely metal-poor star is nearby and bright enough that Gaia will eventually measure the inclination of the system's orbit. It will therefore be possible to measure the mass of the black hole. The low metallicity of the visible star suggests that it and the black hole likely formed long ago, making the black hole a local analog of the stellar mass black holes that seeded the formation of the supermassive black holes observed in the centers of most galaxies.