12.00 noon, Seminar Hall
Quasi-local Black hole Horizons
A black hole space-time is characterised by a region where gravity is so strong that light cannot escape from that region to observers who are outside of it. The boundary of such a region is called an "event horizon". But the notion of an event horizon is global and requires the specification of the complete future evolution of space-time. Hence event horizons cannot be located at any `instant of time'. We will discuss some quasi-local definitions of black hole horizons which can be located at instances of time and are more suited for application in realistic situations. By taking simple examples of mechanical systems we will discuss the spirit of the derivation of the "First Law of Black hole mechanics" in these quasi-local settings.