Gravitational-Wave Versus X-Ray Tests of Strong-Field Gravity*

Electromagnetic observations of the radiation emitted by an accretion disk around a black hole, as well as gravitational-wave observations of coalescing binaries, can be used to probe strong-field gravity. In this talk, I will compare the constraints that these two types of observations can impose on theory-agnostic, parametric deviations from the Schwarzschild metric. I will show that current gravitational wave observations have already placed constraints on the metric deformation parameters than are slightly more stringent than what can be achieved with X-ray instruments in the near future. Moreover, I will show that future gravitational wave observations with aLIGO at design sensitivity by 2026 will be even more stringent, in particular becoming stronger that constraints achievable with future ATHENA X-ray observations in 2034.