Conference

To a first approximation, objects in general relativity move along geodesics. Looked at more closely, a body's internal structure can affect its motion. This talk will explore some of the surprising possibilities which arise when such effects are taken into account. An object can, for example, control its orbit merely by manipulating its internal structure: unstable orbits can be stabilized, bound orbits can be made unbound, and more, all without a rocket.

Since the advent of (relativistic) astrophysics it has been one of the most important tasks to study the motion of freely falling particles, both from a purely academic and an observational point of view. In this presentation I review the solution methods for the equations of motion of particle-like objects and light within a wide variety of spacetimes. Moreover, we take a closer look on the importance of special orbits for phenomena like black hole shadows or accretion discs.

"""Gravitational wave detectors and their increasing precision have enabled more specific tests of general relativity, including spectroscopic tests of black holes by measuring the quasinormal modes within the ringdown signal. These tests ideally compare the QNM frequencies to predictions from theories beyond GR, where black holes may be described by deformations to the Kerr metric. I will present a framework to compute the first order QNM shifts of these deformed Kerr Black Holes at arbitrary spin and present some initial results for the spin-0 case. In addition, I will lay out some of the technical issues that come up when computing the shifts for the spin-2 modes, and explain how they are surmountable."""

We study the stability of quasi-normal modes (QNM) in asymptotically flat black hole spacetimes by means of a pseudospectrum analysis. The construction of the Schwarzschild QNM pseudospectrum reveals: i) the stability of the slowest decaying QNM under perturbations respecting the asymptotic structure, reassessing the instability of the fundamental QNM discussed by Nollert (1996); ii) the instability of all overtones under small scale perturbations of sufficiently high frequency, that migrate to a universal class of QNM branches along pseudospectra boundaries, shedding light on Nollert & Price's analysis (1996).