We show that at any given time , the Galactocentric black hole Sgr A* is expected to be microlensing N _ { lens } \sim 1.7 bulge stars if the threshold of detectability of the fainter image is K _ { thr } = 21 , and N _ { lens } \sim 8 sources if K _ { thr } = 23 .
The lensed images then provide a unique way to detect stellar-mass black holes predicted to cluster around Sgr A* .
If a black hole passes close to a microlensed image , it will give rise to a short ( weeks long ) microlensing event .
We show that the mass and projected velocity of the stellar-mass black hole can both be measured unambiguously from such an event , provided that either a caustic crossing is observed or the astrometric displacement is measured .
For K _ { thr } = 23 and moderate magnifications by Sgr A* , the microlensing event rate from a cluster of 20000 black holes within a radius of 0.7 pc is only 0.06 { yr } ^ { -1 } ; however , if highly magnified images of a star were found , the rate of events by the stellar black holes would be much higher .
In addition , the N _ { lens } sources lensed by Sgr A* provide a unique probe of extinction behind the Galactic center along 2 N _ { lens } lines of sight .