**Shahar Hadar (University of Haifa at Oranim) |** Extreme Black Holes |

Abstract:

The spacetime geometry of a black hole is characterized by a handful of parameters: Its mass, angular momentum, and charge. For a given mass, bounds exist on the maximal possible spin and charge. In the astrophysically relevant neutral case, for example, that bound corresponds to the event horizon spinning at the speed of light. Black holes close to this bound are called (near-)extremal. They display especially remarkable properties, including an emergent conformal symmetry in their near-horizon region. In the talk, I will describe how this symmetry, which was discovered amid attempts to understand quantum black hole properties, can be exploited in order to analytically compute observational gravitational-wave and electromagnetic signatures of near-extremal black holes. Such computations are often practically intractable without an elaborate utilization of the symmetry. The unique near-horizon geometry also explains other peculiar effects occurring in these black holes, such as instabilities developing on their horizons and high-energy particle collisions in their vicinity, which I will describe.

When: December 8, 2021 02:00 PM (Jerusalem).

__Where:__ Multipurpose building, seminar room 223 as well as via Zoom (hybrid format).