Measuring a Black Hole Event Horizon: Very Long Baseline Interferometry of the Galactic Center Sheperd Doeleman, Massachusetts Institute of Technology -- Haystack Observatory

It is now almost certain that at the center of our Milky Way Galaxy lies a super massive black hole - 4 million times more massive than our Sun. Because of its proximity to Earth, this object, known as Sagittarius A*, presents astronomers with the best opportunity in the Universe to spatially resolve and image a black hole Event Horizon. To do this requires using Very Long Baseline Interferometry (VLBI), the technique whereby radio telescopes around the world are linked together in a Global phased array. Very short wavelength VLBI observations have now confirmed structure on ~4 Schwarzschild radius scales within SgrA*. I will describe the instrumentation efforts that enable these observations, discuss what current and future VLBI observations of SgrA* tell us about this closest super-massive black hole, and describe plans for assembling a submm-VLBI Event Horizon Telescope.