I lead a research group at ASTRON, the Netherlands Institute for Radio Astronomy. We work on nanohertz gravitational wave science, design the next generation of radio‑astronomy instruments, and build the pipelines that turn petabytes of telescope data into physics. Pulsars sit at the centre of all of it, as the most precise clocks in the Universe.
I lead the only research group in the Netherlands working on nanohertz gravitational wave astrophysics, based at ASTRON. The programme is supported by over €2M in competitive funding from a European Research Council Starting Grant (project GIGA) together with an NWO-I Veni fellowship.
Our work rests on two main pillars. The first is gravitational wave science. I co-led the European PTA noise analysis that contributed to the first compelling evidence for the gravitational wave background in 2023, work that was recognised with the Frontiers of Science Award and the RAS Group Achievement Award. Research in our group also includes EPTA noise modelling, Gamma-ray PTA methodologies and science, young pulsar timing and ISM modelling.
The second pillar is algorithms and instrumentation. I commissioned MeerKAT’s pulsar timing backend in South Africa and co-founded the Gamma-ray Pulsar Timing Array with M. Kerr, which remains the only independent path to the gravitational wave background outside of radio. I also co-lead a novel phased-array feed design in collaboration with Breakthrough Listen, and a proposal to upgrade the Westerbork dishes into a national radio astronomy facility.
Read more about the programme on the GIGA group page or see the full CV.
We lead research at the frontier of nanohertz gravitational wave science, combining PTA noise modelling , young pulsar timing, and ISM modelling to push the sensitivity of pulsar timing arrays. The group is supported by the GIGA compute cluster at ASTRON, dedicated to large-scale pulsar timing inference.
Gravitational waves crossing the galaxy leave a specific pattern in pulsar timing residuals: pairs close on the sky are correlated, pairs ninety degrees apart are anti-correlated, opposite pairs are correlated again.
This shape — the Hellings–Downs curve — cannot be produced by noise, solar-system errors, or interstellar scattering. It is the deciding signature that the signal we see is a stochastic gravitational-wave background.
Four radio pulsar timing arrays — combined under the IPTA — each watch tens of millisecond pulsars with nanosecond precision. The 2023 evidence was built from >25 years of such data.
When two galaxies merge, their central supermassive black holes spiral toward each other — from kiloparsecs, through dynamical friction, down to a hard binary at sub-parsec scales.
In their final millions of years they radiate continuous gravitational waves squarely in the nanohertz band — too low for LIGO, too low for LISA. The overlap of millions of such binaries across cosmic time forms the stochastic background that pulsar timing arrays are sensitive to.
Adapted from standard binary-inspiral cartoons; orbital separation shown schematically from ~10 pc down to coalescence.
The same millisecond pulsars that radio telescopes time can also be timed using gamma-ray photons from Fermi-LAT — no radio dish, no interstellar plasma, a completely independent systematics chain.
More than ten years of Fermi data set a 95% upper limit of AGWB < 1.0×10⁻¹⁴ — competitive with early radio-PTA results and opening a second, orthogonal window on the same nanohertz sky.
Approximate 95% upper limits on AGWB (×10⁻¹⁴) over time; radio-PTA points adapted from published EPTA / NANOGrav / PPTA / IPTA data releases, gamma-ray point from Fermi-LAT (2022).