At the Center of the Milk Way . ... NACO , ESO Explanation: At the center of our Milky Way Galaxy lies a black hole with over 2 million times the mass of the Sun. ... NACO's ability to track stars so close to the galactic center can accurately measure the black hole's mass and perhaps even provide an unprecedented test of Einstein's theory of gravity as astronomers watch a star orbit a supermassive black hole . ...