Speaker
Description
Black holes are some of the most interesting objects in astrophysics. Light, gravitational waves, and massive particles emitted or passing in their close vicinity are gravitationally lensed and provide a unique probe of gravity in the strong field regime. On one hand this allows to test different black hole models from general relativity or alternative theories of gravity, and on the other hand different theories of gravity themselves. In my talk I will illustrate how we can distinguish different black hole models from general relativity using gravitational lensing of light, high-frequency gravitational waves, and massive particles in the strong field regime. For this purpose I will use three different black hole spacetimes from general relativity: The Schwarzschild spacetime, the Newman-Unti-Tamburino (NUT) spacetime, and the Kerr spacetime. I will first solve the equations of motion analytically using elementary and Jacobi's elliptic functions as well as Legendre's elliptic integrals. Then I will place a standard observer in the domain of outer communication outside the photon region and relate the constants of motion to latitude-longitude coordinates on the observer's celestial sphere. In this parameterisation I will first discuss, for light and high-frequency gravitational waves, the impact of the so-called gravitomagnetic charge and the spin parameter on the observable lensing features, in particular on the lens map, the redshift, and the travel time. In the second part of the talk I will then use the lens map and the travel time to illustrate how the picture changes for massive particles using the Schwarzschild spacetime and the NUT spacetime as examples. Finally, I will discuss how these unique characteristics will allow different ways to probe gravity in the strong field regime and present a short outlook on the final goal of using multimessenger lensing as one component of the Maxwell-Einstein-Pauli Observatory to probe gravity in the strong field regime.
