# Gravitational wave modelling

We model sources of gravitational waves and compute their waveforms. We focus on Extreme Mass Ratio Inspirals (EMRIs), which are binary systems consisting of a primary super-massive black hole (SMBH) and a secondary stellar-mass compact object. In these binaries, the comparably lighter compact object can be viewed as moving in the gravitational field of the primary, where it slowly spirals towards the central black hole. The degradation of the orbit is caused by the loss of energy and angular momentum due to gravitational radiation reaction. Such processes are predicted to routinely occur in the centers of galaxies, where the compact objects enter inspirals around the heavy central black holes due to complicated many-body dynamics of the surrounding dense stellar clusters.

Gravitational waves from EMRIs are promising sources for the space-based gravitational-wave detector LISA (Laser Interferometer Space Antenna). LISA is the L3 mission of ESA in its Cosmic Vision science program currently scheduled for launch in the early 2030s. The EMRI signals detected by LISA will allow us to map the spacetimes around SMBHs. In return, this will also allow us to test whether the gravitational fields of SMBHs are well described by Einstein's General Relativity or not. The current consensus is that gravitational waveform template banks are necessary in order to be able both to detect and interpret the received signal.

In our source modelling we concentrate mainly on the inclusion of astrophysical effects modifying the simplest EMRI models, namely effects due to the finite size of the secondary objects or external gravitational perturbations. In both cases, we employ tools traditionally developed in the fields of dynamical astronomy and non-linear dynamics ranging from Poincaré sections to canonical perturbation theory. For calculating the GW fluxes and the waveforms we use a time domain Teukolsky solver called Teukode developed by Sebastiano Bernuzzi and Enno Harms at the University of Jena, and tools from the Black Hole Perturbation Toolkit.

References

- Harms E.,
**Lukes-Gerakopoulos G.**, Bernuzzi S., Nagar A. (2016) "Spinning test body orbiting around a Schwarzschild black hole: Circular dynamics and gravitational-wave fluxes." Physical Review D 94, 104010 [ads, doi] -
**Lukes-Gerakopoulos G., Kopáček O.**(2018) "Recurrence analysis as a tool to study chaotic dynamics of extreme mass ratio inspiral in signal with noise." International Journal of Modern Physics D 27, 1850010 [ads, doi] -
**Witzany V.**(2019) "Hamilton-Jacobi equation for spinning particles near black holes." Physical Review D 100, 104030 [ads, doi] -
**Zelenka O., Lukes-Gerakopoulos G., Witzany V., Kopáček O.**(2020) "Growth of resonances and chaos for a spinning test particle in the Schwarzschild background." Physical Review D 101 [ads, doi]