Assistant Professor
Radboud University
Hi! I am an Assistant Professor in Physics at Radboud University, where I do research in theoretical physics. In particular, I focus on foundational questions in general relativity and predictions for future gravitational-wave observatories such as the Einstein Telescope and LISA.
I wrote an article about black holes that goes beyond the usual laymen's presentation and gets to the heart of what black holes really are. It is written for high school students in their final years with an interest in physics. So if that is you, go check it out (with my apologies if you don't speak Dutch, as it is written in Dutch). In fact, you may want to check out the website
I have developped a seven-week master course titled "Foundations of gravitational waves and black hole perturbation theory", which I teach every Spring semester (in the third quarter). You are welcome to download the materials for this course:
If you find any typos: first off, my apologies, and second, it would be great if you would let me know!
I'm excited that NWO has chosen to fund my research proposal Observing resonating black holes with gravitational waves.
Since September 2020 the RU Science Faculty offers a Gravity+ synergy track to Master students enrolled in the Master's specialisations of Mathematics and Particle & Astrophysics. The courses reflect Radboud expertise in gravity, ranging from black-hole imaging (Event Horizon Telescope) and gravitational wave astronomy to quantum gravity and mathematical foundations of general relativity. In particular, it provides a solid preparation for research in my group. Click on the link for more information and the image on the left for a short video clip about the program.
For Dutchies only: De Nationale Wetenschapsagenda organiseerde een facebook live event op 7 december 2021 over zwarte gaten, waarin ik allerlei vragen beantwoord van de kijkers samen met Jaco de Swart. Voor een korte teaser, zie dit korte filmpje en het volledige vragen half-uurtje is hier terug te zien.
All my scientific publications are freely available online.
Some of my recent work includes (click on the pictures on the left for a link to the articles):
Black holes have a very specific gravitational field, which one can characterize by its multipole moments. The multipole moments of black holes are all completely determined the mass and spin of the black hole. We asked the question: are there other objects that can mimick all the multipole moments of a rotating black hole? We constructed an explicit example of a Newtonian star with multipole moments identical to those of a rotating black hole, so the answer to this simple question is "yes".
A few years ago, my collaborators and I pointed out that tidal resonances may play an important role for Extreme Mass Ratio Inspirals. In two papers on this topic, we explored the entire parameter space and showed that these resonance leave an observable imprint on the waveform for most EMRI configurations. We also made the first steps needed in order to model these resonances efficiently, which also nicely applies to self-force resonances (how is that for killing two birds with one stone? :)).
Symmetries play a key role in theoretical physics. However, most realistic systems posses no symmetries. Fortunately, if you go far away from a compact object with strong gravity such as black holes and neutron stars, the spacetime becomes approximately flat again. As a result, you do have "asymptotic symmetries". These asymptotic symmetries are described by the Bondi-Metzner-Sachs algebra (BMS) and they play an important role in gravitational science. However, if you take into account that the universe is expanding, the spacetime does not become asympotically flat. We carefully examined what happens if you have spacetimes that expand in a decelerating fashion and found that the asymptotic symmetry algebra of this large classs of spacetimes is like the BMS algebra. However, it is not exactly the same! See the paper for details :)
When two neutron stars are in a binary system, they exert tidal forces on each other. These tidal forces increase as the two stars get closer during their inspiral. As a result, one of the natural modes of the stars -- called the interface mode -- can be resonantly excited. When this happens, the orbital energy is transferred to the star's crust, which can then melt. This all happens during the final phases of the inspiral and we predict that this is observable by future ground-based gravitational wave detectors. This would be cool as it provides more information about the properties of neutron stars and the fundamental properties of nuclear matter at high densities.
This work is the final answer to a long list of papers about angular momentum radiated by electromagnetic and gravitational waves. It all started with a surprising fact about angular momentum radiated in electromagnetism: while one typically thinks of fluxes radiated to infinity to only depend on the radiative degrees of freedom, the total flux of angular momentum radiated also depends on the Coulombic degrees of freedom. These Coulombic degrees of freedom appear through an interaction term between the radiative degrees of freedom and the charge aspect. This occurs in realistic scenarios, for instance, all the angular momentum radiated by a charged spinning sphere with variable angular velocity is due to this interaction term. This is not the case for gravitational waves: the angular momentum radiated by gravitational waves is entirely encoded in the radiative degrees of freedom. This interesting difference between electromagnetism and gravity deserved further explorations, and that is exactly what we did in this paper!
Mean motion resonance is a type of orbital resonance that occurs due to the gravitational interaction between two objects orbiting a central massive object. They are very common in planetary systems, for instance, the moons of Jupiter are in various mean motion resonances. We investigated whether mean motion resonance in the strong gravity regime around massive black holes. During this type of resonance, objects are "locked" and move in a synchronized way. As a result, mean motion resonance can create the perfect circumstances for tidal resonances to occur, which are likely observable by LISA. For a nice layman's description about tidal resonances, see this article in Inside the Perimeter.
If you are a bachelor or master student looking for a thesis project, please send me an email. If you are doing a double bachelor (in particular, physics and mathematics), co-supervision with a supervisor from another department is possible.
This is a selection of some of my recent outreach that has found its way to the worldwide web:
For some movies in which I talk about physics, see these clips in English:
Here is also a movie in Dutch:
Huygens building - Room 02.822
Heyendaalseweg 135
6525 AJ Nijmegen
The Netherlands
IMAPP, Faculty of Science
P.O. Box 9010
6500 GL Nijmegen
The Netherlands