We describe the feasibility of detecting the gravitational deflection of light emitted by stars moving under the influence of the massive object at the Galactic center .
Light emitted by a star orbiting behind the central mass has a smaller impact parameter than the star itself , and suffers the effect of gravitational lensing , providing a closer probe of the central mass distribution and hence a stricter test of the black hole hypothesis .
A mass of 4.3 \times 10 ^ { 6 } M _ { \odot } causes a 0.1 - 2 mas deviation in the apparent position of orbiting stars projected within 10 ^ { \circ } of the line of sight to the galactic center .
In addtion , we may uniquely constrain the distance to the center of the galaxy because lensing deflections constrain the ratio r _ { g } / R _ { 0 } of the Schwarzschild radius to the distance to the black hole , R _ { o } , whereas the ratio r _ { g } / R _ { o } ^ { 3 } is obtained by fitting the orbit .