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 gave a talk about black holes and the cosmos for Radboud Reflects at De Kaaij, a lovely spot on the river Waal underneath the old Waalbrug in Nijmegen, with a clear view of the night sky. We talked about what black holes are, how they work, and how we detect them (did you know that to turn the Earth into a black hole, you would have to compress it into a marble measuring just 5.5 centimeters across?). You can read more about the event here.
I got interviewed by Radboud Recharge about my research, the Skywalk audiotour (see above) and my career path. You can read the interview here.
My first PhD students, Ariadna Ribes Metidieri & Patricia Ribes Metidieri (yes, they are identical twins!), defended their PhD theses cum laude in June. A spectacular result! A nice article appeared at Radboud Recharge about their achievement. In summer, Ariadna will join the Niels Bohr Institute in Copenhagen and Patricia will join the QFT group at the University of York.
I am honored to have been awarded the Radboud Science Award. The award ceremony for the Radboud Science Award was fantastic: the entire aula filled with enthusiatic elementary school students. I have never experienced so much energy during a scientific event.
Registration is open for our two-year master's programme at Radboud University that includes the specialization ("synergy track") Gravity+. In addition to a standard curriculum in Particle & Astrophysics or Mathematics, students have access to a unique combination of courses on modern aspects of gravity, from classical to quantum, from mathematical to astrophysical, covering black holes, gravitational waves, quantum gravity and much more. Visit gravityplus.org for more information and how to apply. You can also click on the image on the left for a short video clip about the program. Motivated students from non-EU/EEA countries can apply for the Radboud Scholarship Programme . This programme significantly reduces the tuition fees for non-EU/EEA students. The Radboud Scholarship can be combined with the NL Scholarship , which provides an additional €5,000 award for non-EU students pursuing a master’s degree at Radboud University.
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):
Yay, our paper about nonlinear effects in black holes got in PRL and published on Valentine's day 💛! After two black holes merge, they create a new distorted black hole. This distorted black hole will absorb gravitational radiation to settle down to a standard vanilla black hole. This radiation is well described by damped sinusoids with very specific frequencies, called quasi-normal modes (QNMs). These frequencies can be predicted using black hole perturbation theory. As it turns out, to match observations better, we need to work upto second order in perturbation theory! It was thought that the ratio of second order amplitudes to the linear parent amplitudes sourcing them would be initial data independent, but we showed that this is not quite true.
Gravitational lensing in the wave optics regime is a new endeavor of mine. It is a beautifully rich field combining caustic singularities, general relativity and interference phenomena. Here we explore the interference patterns you get from a rotating lens.
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.
I have developed 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!Over the years, I have developed lesson plans and educational materials for schools, and I regularly visit elementary and high schools to talk about black holes and gravitational waves. Below is an overview of these activities and resources.
I developed a 1,5 hour long lesson plan about black holes for children in the last two years of elementary school (in the Dutch system: groep 7 en 8), in collaboration with Science Hub Radboud University. The lesson plan is freely available here (sorry, only in Dutch at the moment). I have already taught it in more than 10 different classes, including at elementary schools "de Akker" and "de Hazensprong" in Nijmegen. The kids were amazing and super engaged every time. So spread the word and try it yourself!
For some movies in which I talk about physics for the classroom, see these clips (in English):
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:
Huygens building - Room 02.731
Heyendaalseweg 135
6525 AJ Nijmegen
The Netherlands
IMAPP, Faculty of Science
P.O. Box 9010
6500 GL Nijmegen
The Netherlands