| We propose to measure the mass of the central black hole in a distant (z1) galaxy, through its
gravitational lensing e ect. Our target is a lensing galaxy that is known to produce three images of a background
quasar. A supermassive black hole would produce a faint fourth image, whose and position depend on the black
hole mass. We will search for this fourth image with sensitive VLBI imaging. With the VLBA, Green Bank Telescope,
and phased VLA at 3.6 cm, we will have suÆcient collecting area and angular resolution to detect the fourth image,
if the black hole has the mass that one would expect from studies of nearby galaxies. This would be the rst
observation of lensing by a supermassive black hole, and the rst direct detection of a black hole in an inactive
galaxy at signi cant redshift. |
