Probing black hole physics with gravitational waves

It has been just over a decade since the first detection of gravitational waves (GWs) from a binary black hole (BH) merger, which opened an entirely new observational window into the Universe. Since then, we have already observed more than 300 merger events, a number that roughly doubles with each new observational run. With the next generation of gravitational wave detectors such as the Einstein Telescope (ET) and the Laser Interferometer Space Antenna (LISA), we are entering an exciting era of BH exploration and precision tests of general relativity (GR) in the strong-field regime.

The coalescence of two BHs involves three stages: the inspiral phase, during which the two BHs orbit each other and progressively get closer; the merger phase, when they collide to form a single, larger BH; and the ringdown phase, during which the newly formed BH relaxes into the stationary state by emitting GWs characterized by a set of exponentially damped harmonic oscillations known as quasinormal modes (QNMs). Successful detection and correct interpretation of real GW signals require careful and precise modelling of all three stages. While these are primarily determined by the properties of the binary system, increasingly sensitive GW detectors may reveal additional effects arising from the surrounding astrophysical environment or potential deviations from GR.

The student will join the Relativistic Astrophysics Group (astro.cas.cz) at the Astronomical Institute of the Czech Academy of Sciences and will have the opportunity to work on various aspects of the BH coalescence based on the student’s interests, such as modelling the long-term evolution of binary orbits, investigating transient phenomena or environmental effects that influence the inspiral, or exploring effects that affects the ringdown and its characteristic frequencies. The project will involve an extensive use of analytical and numerical methods, potentially including machine learning.

References:

[1] C. Berry et al. (2019): The unique potential of extreme mass-ratio inspirals for gravitational-wave astronomy
[2] T. Hinderer and É. É. Flanagan (2008): Two-timescale analysis of extreme mass ratio inspirals in Kerr spacetime: Orbital motion, Phys. Rev. D 78, 064028
[3] A. Abac et al. (2025): The Science of the Einstein Telescope
[4] T. Damour, A. Nagar (2016): The Effective-One-Body Approach to the General Relativistic Two Body Problem, Lect. Notes Phys., vol 905, Springer, Cham
[5] N. Franchini, S. H. Völkel (2024): Testing General Relativity with Black Hole Quasi-normal Modes