List of PhD projects available

An overview

There will be several PhD positions open for application with a deadline of November 15, 2026. For details of the application procedure see this page. The PhD positions that are offered this round are listed below. The faculty research interests provides more background information about the research conducted at the Leiden Observatory.

  • PhD project 1: Understanding the Population of Cosmological Radio Transients -- Explainable AI on LOFAR and Westerbork
    Supervisor: Joeri van Leeuwen
    Description: The Universe was long thought to be mostly static, changing only on timescales of millions of years. This view changed with the discovery of fast radio bursts (FRBs) and gravitational waves (GWs). These explosions point to energies, densities, and space-time curvature that far exceed any terrestrial laboratory.
    Much of the physics driving these catastrophic events remains a mystery due to great observational challenges: the radio and gravitational-wave bursts are visible for milliseconds only. The measurement data rates produced by LOFAR and Westerbork exceed those of entire countries, and need to be processed in real time to react quickly, and even to keep up. We have pioneered the use of AI to mitigate this large data pressure. This was very successful, and we now know there is a population of transients out there that could be used to measure the invisible contents of the Universe. But one open question remains: our AI found only one-off FRBs, and no repeating FRBs, although we know those exist, so
    Does this reflect the true prevalence of repeating sources in the FRB population, or is it AI bias?
    In this project, a collaboration between ASTRON and Leiden University, we will tackle one of the main open questions in the field: do one-off and repeating FRBs represent two physically different sources? If so, which ones? Hypotheses range from precession to plasma lensing, and binary interactions. To answer this ambitious but fundamental question, we need to trust the ability of our classifiers to find both kinds of FRBs, in data from LOFAR and Westerbork now, and for SKA in the very near future.

  • PhD project 2: Developing the technology for the characterization of Earth 2.0
    Supervisor: Sebastiaan Haffert
    Description: The next frontier in astronomy is an age-old question: is there other life in the universe? Europe’s upcoming Extremely Large Telescope (ELT) and Large Interferometer For Exoplanets (LIFE) and NASA’s Habitable World Observatory (HWO) have the search for life in the universe as their top priority science case. Searching for biosignatures in the atmospheres of other planets is a very challenging observation and it requires instruments that make optimal use of all photons that are collected. However, there is still a technological gap between the performance of our current optical designs and the fundamental limits of physics in terms of sensitivity and resolution. The PhD candidate will develop new technologies such as photon-counting IR coronagraphic systems for HWO and ELT, develop new coronagraphic components or new kinds of super-resolution imaging techniques and test these on the largest telescopes on Earth. In this project the applicant will work together with Dr. Sebastiaan Haffert and collaborators to bring our instruments to the limits.

  • PhD project 3: 3D simulations of star-planet interactions
    Supervisor: Aline Vidotto
    Description: Star-planet interactions in exoplanetary systems can occur under substantially different regimes than the ones encountered in solar-system planets. These interactions are mediated by host-stars' particle, magnetic and high-energy radiation fields. High-energy radiation heats planetary atmospheres, which inflate and more likely escape. Stellar particle outflows cause pressure confinement around otherwise freely escaping planetary atmospheres. Stellar and planetary magnetism affect the energetic budget available to power the interactions. Can we detect signatures of star-exoplanet interactions? How do these interactions affect close-in exoplanets and their atmospheres/magnetospheres?
    To tackle questions like these, we are looking for a motivated PhD student to work on the theme of "star-planet interactions" through 3D simulations. The PhD candidate will use and develop novel 3D magnetohydrodynamic simulations to interpret and guide observations linked to star-planet interactions. Our group has expertise in investigating both the host star (simulating magnetised stellar winds and coronal mass ejections) and the exoplanet (simulating magnetised atmospheric escape), and different projects during the PhD will investigate these aspects. To learn more about the research of our group, please see our webpage: https://avidotto.github.io/.

  • PhD project 4: Clouds on the Giant Planets: A New Physical Framework from Jupiter to Neptune
    Supervisor: Yamila Miguel
    Description: Clouds are among the most visible yet poorly understood features of the giant planets. Years of JWST observations (Giant-planet Atmospheres programme for JWST, PI: Fletcher) are revealing the clouds of Jupiter, Saturn, Uranus and Neptune in unprecedented detail, while major puzzles remain unexplained. In Jupiter, Juno has revealed a strong depletion of sodium and potassium at ~100 bar whose origin remains unknown; deep clouds could provide the missing mechanism by sequestering these elements. In Uranus and Neptune, cloud formation can inhibit convection and produce radiative or stably stratified regions, altering atmospheric heat transport. Clouds may therefore influence not only what we observe, but also the chemistry, thermal structure and evolution of the giant planets.
    Despite their importance, clouds are commonly modeled using simplified treatments in which particles settle while turbulent diffusion mixes material upward. This treats cloud transport as a local diffusive process, whereas clouds often form within organized convection. Bulk-plume models, originally developed for Earth's atmosphere and now being extended within the Simons Foundation collaboration Multiscale Physics of Clouds Across Planetary Atmospheres, offer a physically motivated alternative. They explicitly model rising cloudy plumes and their entrainment and detrainment, predicting cloud mass, vertical velocities, cloud-top pressures and atmospheric structure.
    This PhD project will apply this novel cloud treatment systematically to Jupiter, Saturn, Uranus and Neptune. These planets provide a unique comparative laboratory, spanning very different internal heat fluxes, compositions, gravities, irradiation levels and dynamical regimes. The student will determine how these differences control cloud formation and structure, convection and heat transport. The models will be confronted with observations from JWST, spacecraft missions and ground-based facilities, testing whether this new framework can reproduce observed cloud structures and help resolve outstanding problems in giant-planet atmospheres. Ultimately, the project will establish how clouds couple atmospheric composition, convection and thermal evolution across the Solar System's giant planets.
    The project will be embedded within the international Simons Foundation collaboration Multiscale Physics of Clouds Across Planetary Atmospheres, bringing together 10 experts in Earth, Solar-System and exoplanet cloud physics. The collaboration is developing the bulk-plume framework and identifies the Solar-System giants as key applications of this new approach. The PhD student will work directly with the developers of the methodology and an international network spanning cloud microphysics, atmospheric dynamics, observations and planetary evolution.

  • PhD project 5: Extracting Binary Black Hole Signals from Gravitational-Wave Data
    Supervisor: Lorenzo Speri
    Description: Gravitational-wave astronomy has opened a new window on the Universe by allowing us to detect and study black-hole binaries through observatories such as LIGO-Virgo-KAGRA (LVK) and Pulsar Timing Arrays (PTA), and, in the future, the space-based LISA mission. As detectors become more sensitive and the number of observations increases, the resulting datasets grow richer and harder to analyse.
    Signals may be weak, long, and overlapping, making them difficult to disentangle from detector noise that is itself hard to characterise. Extracting reliable information from this data therefore requires new approaches that combine physical models with modern statistical and computational techniques.
    In this project, you will develop advanced modelling, detection, and characterisation methods for extracting binary black hole signals from gravitational-wave data, with applications to LVK, PTA, and LISA observations, drawing on Bayesian inference, machine learning, signal processing, and high-performance computing. The work will focus on recovering weak signals, disentangling overlapping sources, and rigorously quantifying the uncertainty of the resulting measurements.
    The methods developed will strengthen the analysis of current gravitational-wave observations and help prepare the field for the far larger, more complex datasets expected from future detectors. Ultimately, the goal is to turn challenging observations into robust measurements of binary black hole parameters and investigate their astrophysical origins.
    The project is particularly well suited to candidates with a background in physics, astronomy, applied mathematics, or data science, strong programming skills, and a strong interest in astrophysics, statistics, and General Relativity.

  • PhD project 6: Galaxy Clusters at Ultra-Low Frequencies with LOFAR VLBI
    Supervisor: Reinout van Weeren
    Description: Galaxy clusters are the largest gravitationally bound structures in the Universe and provide unique laboratories for studying the evolution of radio galaxies and their interaction with the surrounding intracluster medium. High-resolution radio observations have revealed intriguing narrow synchrotron filaments and complex structures associated with active galactic nuclei (AGN), but their origin and connection to the evolution of relativistic plasma remain poorly understood.
    This PhD project will exploit the upgraded Low Band Antennas (LBA) of LOFAR2.0 to study galaxy clusters using LOFAR very long baseline interferometry (VLBI), providing sub-arcsecond resolution at frequencies below 100 MHz. This unprecedented combination of low frequency and high angular resolution will probe low-energy populations of relativistic particles, enabling investigations of the history of AGN activity, the survival and evolution of fossil radio plasma, and the origin of narrow synchrotron filaments in cluster environments.
    A key component of the project will be developing and applying advanced calibration and imaging techniques for LOFAR LBA-VLBI observations. These present significant technical challenges, particularly due to ionospheric effects and the large volumes of data involved. The resulting high-resolution images will be combined with higher-frequency radio observations and multi-wavelength data to connect small-scale radio structures to the larger-scale evolution of AGN and their environments.
    The project is suited to candidates with a strong interest in extragalactic astrophysics, radio astronomy, and/or computational methods. It will involve developing and applying state-of-the-art techniques and analysing large datasets using high-performance computing, while contributing to opening up a largely unexplored observational window on galaxy clusters.

  • PhD project 7: The Radio Life of Galaxy Clusters: From Active Galaxies to Diffuse Emission
    Supervisor: Reinout van Weeren
    Description: Radio observations provide a unique view of the relativistic particles and magnetic fields that permeate galaxy clusters, from individual radio galaxies to large-scale diffuse emission in the intracluster medium (ICM). While previous studies have provided detailed insights into individual systems, systematic investigations of larger cluster samples, combining broad frequency coverage and polarimetric information, remain relatively limited. This is particularly true for relaxed clusters, where the origin of extended diffuse radio emission, including radio haloes in the absence of major mergers, remains poorly understood.
    This PhD project will combine wideband radio observations from facilities such as LOFAR2.0 and MeerKAT, with an outlook towards the Square Kilometre Array (SKA) and other future telescopes. By bringing together observations across a broad range of frequencies, the project will move beyond individual case studies towards systematic investigations of the radio properties of galaxy clusters. Spectral and polarimetric information will provide new ways to study relativistic particle populations and magnetic-field structures in both diffuse cluster emission and individual radio galaxies.
    Several complementary research directions are possible within the project. One focus will be to investigate the origin and properties of extended diffuse radio emission in relaxed clusters, where the presence of large radio haloes challenges our understanding of how relativistic particles and magnetic fields are generated and sustained in the ICM. Another direction will be to study the radio populations of cluster galaxies, including AGN and star-forming galaxies, and their connection to the cluster environment by combining radio observations with optical and near-infrared data from Euclid.
    The project will offer opportunities to combine observational radio astronomy, multi-wavelength studies, and the development of new techniques for wideband spectral and polarimetric imaging. It is suited to candidates with a strong interest in observational astrophysics, galaxy evolution, and/or radio astronomy, and will involve working with large astronomical datasets and high-performance computing.

  • PhD project 8: Reliable spectroscopy of exoplanet atmospheres in the ELT era
    Supervisor: Ignas Snellen
    Description: Exoplanet research is entering a new and exciting phase. After decades of discovering planets around other stars, we can now begin to ask what these worlds are actually like: whether they have atmospheres, which molecules they contain, how their climates behave, and how atmospheres survive or escape under intense stellar irradiation. JWST is opening the first detailed window onto small-planet atmospheres, while the Extremely Large Telescope will soon provide a major leap in sensitivity from the ground. The challenge is no longer only to detect faint signals, but to demonstrate that they are real, robust, and physically meaningful.
    This PhD project will focus on high-resolution spectroscopy of exoplanet atmospheres. Planetary signals are extremely weak, but they move in velocity during an observation, while much stronger telluric, stellar, instrumental, and residual halo structures are fixed or vary only slowly. Modern analysis methods can suppress these contaminants, but they can also partly distort or remove the planet signal itself. The project will therefore develop and test signal-preserving approaches, using injection-and-recovery experiments, noise-only tests, realistic simulations, and statistical criteria for deciding when a detection, variability claim, or upper limit is reliable.
    The work will begin with existing high-resolution and JWST data sets, and will then feed directly into preparation for ELT/METIS, the first-generation mid-infrared instrument on the Extremely Large Telescope. The student will help define how future METIS observations of small planets should be analysed, what performance is required for robust atmospheric constraints, and how early benchmark data can validate the methods on sky. In the final stage, the methods will be connected to physical interpretation: what do reliable detections or non-detections tell us about atmospheric composition, structure, escape, and evolution?
    The project is suited for a student interested in exoplanets, spectroscopy, data analysis, and statistical inference. Experience with Python and astronomical data is useful; curiosity, careful thinking, and enthusiasm are essential.

  • Leiden De Sitter Fellowship
    Description: The fellowship is designed to attract exceptionally talented and ambitious early-career researchers and to provide them with an environment in which they can develop into independent scientists, while benefiting from the breadth and strength of the research programmes at LION and STRW.
    A distinctive feature of the de Sitter Fellowship is its cross-departmental character. Rather than being recruited for a single predefined project, the successful candidate will have the opportunity to choose among a portfolio of collaborative research projects developed jointly by researchers at LION and STRW. Each project will be supervised by advisors from both institutes (at least one from each), giving the fellow access to complementary expertise, research communities, and scientific perspectives.
    The possible projects will span areas in which fundamental physics and astrophysics naturally meet, including, for example, cosmology, gravitation, particle and astroparticle physics, compact objects, gravitational waves, large-scale structure, dark matter and dark energy, and the physics of the early Universe. Fellows will be embedded in both institutes and encouraged to participate actively in their scientific life, including seminars, group meetings, workshops, visitor programmes, and international collaborations.
    An important goal of the fellowship is to foster scientific independence from the beginning of the PhD. While each fellow will benefit from close mentoring by two supervisors, they will be encouraged to shape the direction of their research, develop their own ideas, establish collaborations across Leiden and beyond, and progressively build an independent scientific profile.
    The dual-supervision structure is therefore intended not simply as joint supervision, but as a platform for creating new scientific connections between LION and STRW and for allowing fellows to develop research programmes that transcend traditional disciplinary boundaries.
    https://leidendesitter.nl/de_Sitter/Welcome.html