Relativity Seminar
of the Institute of Theoretical Physics

Seminar is held on Tuesdays at 13:10 pm in the lecture room of the Institute
on the 10th floor of the department building at Trója, V Holešovičkách 2, Prague 8

May 28, 2019
Gravitational radiation and evolution of gravitational collapse in cylindrical symmetry
Dr. Alfonso García-Parrado Gómez-Lobo

Using the Sparling form and a geometric construction adapted to spacetimes with a 2-dimensional isometry group, we analyse a quasi-local measure of gravitational energy. We then study the gravitational radiation through spacetime junctions in cylindrically symmetric models of gravitational collapse to singularities. The models result from the matching of collapsing dust fluids interiors with gravitational wave exteriors, given by the Einstein-Rosen type solutions. For a given choice of a frame adapted to the symmetry of the matching hypersurface, we are able to compute the total gravitational energy radiated during the collapse and state whether the gravitational radiation is incoming or outgoing, in each case. This also enables us to distinguish whether a gravitational collapse is being enhanced by the gravitational radiation.

Work done in collaboration with Dr. Filipe Mena (University of Lisbon).

May 31, 2019
!!! ON FRIDAY FROM 10:40 !!!
What is the surface of a black hole?
Prof. José M.M. Senovilla
Theoretical Physics and Science History Department, University of País Vasco, Bilbao

Black holes are fundamental objects in equilibrium predicted by General Relativity. However, in reality, black holes form, evolve and eventually evaporate, thus they are dynamical. Do they have a boundary? If so, where it is? For dynamical black holes, the usual Event Horizon is global and teleological, thus not well defined. One can then resort to using the local concept of closed trapped surface to try and define the surface of black holes, leading to the concepts of dynamical and trapping horizons. We will show the fundamental problems inherent to dynamical or trapping horizons. The trapped region and its boundary will then be introduced, and the difficulties in finding them highlighted. Finally, the concept of core of a black hole will be briefly discussed.

July 2, 2019
Thermodynamics of Lorentzian Taub-NUT spacetimes
Dr. David Kubizňák
Perimeter Institute for Theoretical Physics, Waterloo, Ontario, Canada

I will show how to formulate consistent thermodynamics of the Lorentzian Taub-NUT spacetimes, maintaining (as recently shown relatively harmless) Misner strings. The obtained first law is of full cohomogeneity and allows for asymmetric distributions of Misner strings as well as their potential variable strengths -- encoded in the gravitational "Misner charges". Notably, the angular momentum is no longer given by the Noether charge over the sphere at infinity and picks up non-trivial contributions from Misner strings.

Jiří Bičák                                                                                                  Oldřich Semerák