Model independent tests of the Kerr bound with extreme mass ratio inspirals

Understand

An outstanding prediction of general relativity is the fact that the angular momentum $S$ of an isolated black hole with mass $\mu$ is limited by the Kerr bound, $S\leq G\mu^2/c$.

• Testing this cornerstone is challenging due to the difficulty in modelling spinning compact objects that violate this bound.
• We argue that precise, model-independent tests can be achieved by measuring gravitational waves from an extreme mass ratio inspiral around a supermassive object, one of the main targets of the future LISA mission.
• In the extreme mass ratio limit, the dynamics of the small compact object depends only on its multipole moments, which are free parameters.