Nearby Stars as gravity detectors

The Essay "How fast can a black hole rotate?", by C. Herdeiro and E. Radu, was selected for an "Honorable Mention" in the Gravity Research Foundation 2015 Awards for Essays on Gravitation. It is the second consecutive year an essay from our group gets this distinction. The first prize was awarded to the Nobel Laureate Gerard 't Hooft, for the essay "Local Conformal Symmetry: the Missing Symmetry Component for Space and Time".
Abstract: It is well known that electromagnetic and gravitational waves scatter as well as get converted to one another by a charged black hole. We demonstrate that the electromagnetic and gravitational scattering and conversion cross s