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
Due to spectacular advances in observational astronomy, strong evidence for the existence of dark massive compact objects has accumulated over the last few decades, thus gradually shifting our perception of black holes from purely mathematical entities to potentially real physical objects. However, event horizons are not physically observable, and therefore the question of whether the observed astrophysical black holes candidates are genuine black holes is still open. To alleviate the pathologies associated with event horizons, I will present dynamical black hole solutions built from the assumption that a regular quasilocal (e.g., apparent or trapping) horizon forms in finite asymptotic time (i.e., according to the clock of a distant observer). Taking this as the only requirement within the semiclassical framework, the spherically symmetric Einstein field equations admit only two distinct families of real-valued dynamical solutions, namely evaporating black holes and accreting white holes. Both of them violate the null energy condition near the outer horizon. I will derive their properties and present the physical implications.
In standard General Relativity, gravitational waves have only two tensor polarisations. However, many alternative theories of gravity predict the existence of additional scalar or vector modes. In this talk, I will present the capability of LISA to constrain extra gravitational-wave polarisations emitted by supermassive black hole binaries. By employing the parametrized post-Einsteinian (ppE) framework, we quantify deviations from GR and map the polarisation parameters to specific modified gravity theories, allowing us to place constraints on fundamental theory parameters or their combinations.
It is known that linearized perturbations of extremal black holes result in growing curvature on the horizon. However, nonlinear perturbations typically do not evolve to extremal black holes and do not have growing curvature at late times. We show that a large class of nonlinear perturbations of an extremal planar anti-de Sitter black hole does have horizon curvature that grows unbounded in time. The late time behavior of the nonlinear evolution is found to be captured by a linearized analysis. We argue that the generic nonlinear perturbation behaves similarly.
David Kubizňák Oldřich Semerák