Speaker: Dr. Torben Frost (NTNU)
Talk title: Gravitational Lensing in Black Hole Spacetimes of the Plebanski-Demianski Class
Time: 2026/09/07 (Mon.) 12:30
Place: NCTS Physics 4F Lecture Hall, Cosmology Hall, NTU

Abstract: 
When photons travel close to a black hole their paths can significantly deviate from those in a flat space vaccum. As a result images of sources or source distributions will be distorted, and how they are distorted depends on the physical properties of the black hole. In my talk I will discuss such distortion effects based on six black hole solutions from Einstein's electrovacuum field equations which are all special cases of the so-called Plebanski-Demianski spacetime, namely the Schwarzschild spacetime, the Reissner-Nordström spacetime, the Schwarzschild-de Sitter spacetime, the C-metric, the NUT metric, and the Kerr spacetime. Here, I will first briefly demonstrate how one can solve the equations of motion analytically exact. Then I will use the solutions to write down a lens equation, and to calculate the redshift and the travel time. I will discuss how we can use them to determine the physical parameters characterising a black hole. In the final part of my talk I will then briefly discuss the impact of a plasma and how one can systematically develop the presented work into a multimessenger approach for probing gravity in the strong field regime.