Gyroscope precession as an indicator of a Kerr horizons

The spin of a gyroscope when placed in a rotating spacetime undergoes precession, due to
frame-dragging. The Kerr solution, which is one such rotating spacetime, describes a
rotating black hole or a naked singularity, depending on the dimensionless angular
momentum parameter. In this talk I will discuss how, for a class of observers, these
precession frequencies diverge on the event horizon of a black hole but are finite and
regular for a naked singularity, everywhere except at the singularity itself. Although
the precession frequency diverges in both cases, I will show that they have
characteristic features that can be used to tell them apart. These are
coordinate-invariant effects and therefore can be interpreted as a genuine test of the
existence of an event horizon.