Astro2020 Science White Paper: A New Era for X-ray Lensing Studies of Quasars and Galaxies

Current X-ray observations and simulations show that gravitational lensing can be used to infer the structure near the event horizons of black holes, constrain the dynamics and evolution of black-hole accretion and outflows, test general relativity in the strong-gravity regime and place constraints on the evolution of dark matter in the lensing galaxies. These science goals currently cannot be achieved in a statistically large sample of z = 0.5 - 5 lensed quasars due to the limited capabilities of current X-ray telescopes and the relatively low number (~200) of known lensed quasars. The latter limitation will be resolved with the multi-band and wide-field photometric optical survey of LSST that is expected to lead to the discovery of u003e 4,000 additional gravitationally lensed systems. As we show in this white paper, these science goals can be reached with an X-ray telescope having a spatial resolution of 0.5 m^2 at 1 keV.