Black-hole astronomy as a probe of fundamental physics

Current observations in black-hole astronomy could offer new pathways to constrain deviations from General Relativity. This includes tests of black-hole uniqueness, black-hole stability, and corrections at strong curvature.

• The uniqueness frontier: Recent VLBI observations of supermassive black-hole shadows present a novel test of black-hole uniqueness. Here, I will focus on the key challenge to disentangle geometry from astrophysics.
• The stability frontier: The linearized dynamics determines the onset of potential instabilities. Here, I will discuss how said instabilities can constrain the presence of additional degrees of freedom.   
• The curvature frontier: The nonlinear regime of binary mergers probe gravitational dynamics at strong curvature. Here, I will present recent progress on well-posed nonlinear evolution in Quadratic Gravity, i.e., for the leading-order curvature corrections to General Relativity.

Throughout, I will advocate that progress requires close collaboration between researchers in observational astronomy and fundamental physics.