Wednesday Colloquium


"Slowly rotating Schwarzschild star beyond the Buchdahl limit"

Camilo Posada (Institute of Physics Faculty of Philosophy and Science Silesian University in Opava)

The Schwarzschild interior solution, or ‘Schwarzschild star’, for a spherically symmetric mass with constant energy density, shows a divergence in pressure when the radius of the star R = (9/4)M. Recently, Mazur and Mottola showed that this divergence is integrable, inducing non-isotropic transverse stresses on a surface of some radius R0. When this radius approaches the Schwarzschild radius, the interior solution becomes one with negative pressure and no event horizon, which resembles a gravastar. Using Hartle’s structure equations, for equilibrium configurations in slow rotation, we report results of surface and integral properties for a slowly rotating Schwarzschild star beyond the Buchdahl limit, RS < R < (9/8)RS, where RS is the Schwarzschild radius. We found that quantities like the moment of inertia I, and the mass quadrupole moment Q approach to the corresponding values for the Kerr metric to second order in the angular velocity. These results provide a solution to the problem of the source of a slowly rotating Kerr black hole.


"Redefinition of the kg"

Krzysztof Łazowski (Mass Laboratory, Central Office of Measures, Warsaw)

In the speech we will discuss issues with the present definition of the kg and efforts to overcome them. We become acquainted with recommendations for the redefinition of the kg, revised SI system based on fundamental constants of nature and realization of a definition of the kg. Finally we will talk about dissemination of the mass unit, air–vacuum transfer and establishing traceability to the new kilogram.


"What was the last Nobel Prize in physics given for?"

Czesław Radzewicz (Department of Physics, Warsaw University)