List of PhD projects available

An overview

There will be several PhD positions open for application with a deadline of November 15, 2025. 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: Using optical metamaterials to create hybrid coronagraphs
  Supervisor: Sebastiaan Haffert
  Description: Imaging Earth-like planets is challenging due to the overwhelmingly large difference in brightness between a planet and its host star. Coronagraphs are specialized optical systems that filter out this star light to reveal faint exoplanets. However, any instrumental error will cause light from the star to leak through the system creating speckles that difficult to distinguish from planet light. We will leveraging optical metamaterials, an exciting new class of optical components, to develop hybrid coronagraphs that both act as a coronagraph and as a wavefront sensor. This will allow us to measure the deformations in starlight and use active control to remove the deformations. Optical metasurfaces, constructed with nanoscale structures using advanced lithographic techniques, provide unparalleled manipulation of their optical characteristics. This capability allows them to surpass previous limitations in the design of coronagraph components. In this project the applicant will work together with Dr. Sebastiaan Haffert to develop optical meta-material components for the Extremely Large Telescope (ELT). The new technology will be tested on-sky at world-leading observatories to demonstrate their potential for the ELT.
  
  
• PhD project 2: Dissecting the complexity of Planetary Nebulae in 3D
  Supervisor: Ana Monreal Ibero
  Description: Galactic Planetary nebulae (PNe), the final evolutionary stages of stars with initial masses between 0.8 and 8.0 M☉, play a key role: i) in our understanding of last stages of the stellar evolution; ii) in the (re)cycling in ISM of processed material within the stars, and by extension the chemical evolution of the Galaxy (and the Universe); iii) as self-contained laboratories to study the physics of ionised plasmas, thus acting as corner-stone targets for our study of the ISM in its broadest sense; iv) as templates for extra-galactic PNe to understand the properties of galaxies other than ours.
  
  PNe are far from simple entities. They exhibit different levels of symmetry, and within a single PN, a wide range of structures may be found with varying degree of ionisation, density, size, shape and composition. In this sense, the information collected by traditional techniques can be misleading since they sample only a small subset of the existing ions (narrow filter imaging) or selected portions of the nebula (long-slit spectroscopy). A handful of studies of individual targets have demonstrated that Integral Field Spectroscopy is able to capture this richness in terms of structure, and physical and chemical properties. However, we are just seeing the tip of the iceberg: there is a need for a spatial-spectral study making use of high-quality data for a sample of PNe, covering a representative range of morphologies, abundances, ages and stellar masses. This project aims to fill this gap. In this project, the student will unveil the hidden complexity of planetary nebulae in 3D by using the state-of-the-art spectroscopic instrumentation in astrophysics. It will be possible reveal previously unknown structures within the studied PNe and map their physical and chemical conditions in 2D. The data gathered will provide the most complete description of a PN and its multiple phases, allowing us to recover the full picture of the PNe with unprecedented detail through 3D photoionization modeling.
  
  
• PhD project 3: Next steps in the characterisation of exoplanet atmospheres
  Supervisor: Ignas Snellen
  Description: Characterisation of exoplanet atmospheres is going through a rapid revolution. JWST is transforming our understanding of increasingly smaller and cooler planets. Soon the Extremely Large Telescope will see first light that will move the field even further. In this PhD project, you will work with state-of-the-art techniques, such as spectral filtering, cross-correlation methods, and molecular mapping on either space-based or groundbased data, or both. We are slowly but surely pushing towards planets that could be like Earth and find out what they are like.
  
  
• PhD project 4: The molecular ISM at high-redshift
  Supervisor: Jacqueline Hodge
  Description: Tracing the evolution of gas in galaxies is critical for a complete understanding of galaxy formation. Recently, huge strides have been made on this front both observationally and theoretically. And yet, most observations of distant (z>1) galaxies still rely on high-J CO emission lines, which are known to give a biased and incomplete view of the total molecular gas reservoir. In this project, we will use recently awarded observations on the VLA/ALMA, as well as ultimately ALMA Bands 1 & 2, to directly detect and resolve the critical low-J CO (and [CI]) lines in a significant sample of z~2-5 galaxies. Specifically, we will: 1) Obtain robust total molecular gas masses, gas fractions, and consumption timescales, free from excitation bias; 2) Calibrate alternative cold gas mass tracers including long-wavelength dust continuum, [CI], and [CII]158μm emission in galaxies spanning a range of redshifts and physical conditions; and 3) Combining with JWST observations & resolved follow-up, provide the first high-resolution, multi-tracer view of the stellar mass (past), star formation (present), and cold gas (future) of individual high-redshift galaxies with which to test the latest hydrodynamical simulations that resolve cold gas in high-z galaxies (eg COLIBRE).
  
  
• PhD project 5: Cosmic-Ray Acceleration and Radio Filaments in Galaxy Clusters with LOFAR2.0
  Supervisor: Reinout van Weeren
  Description: Galaxy clusters are the largest virialized cosmic ecosystems in the Universe—and they also act as gigantic particle accelerators. In addition to galaxies and dark matter, clusters are filled with hot plasma, magnetic fields, and cosmic rays: highly energetic particles that emit synchrotron radiation detectable with modern radio telescopes. A key open question is how these cosmic rays are accelerated and how they interact with the surrounding plasma. Recent observations have also revealed puzzling, extremely narrow filamentary radio sources in clusters, whose origin remains unknown.
  
  This PhD project will exploit the revolutionary capabilities of the upgraded LOFAR2.0 radio telescope to tackle these questions. LOFAR2.0 opens a new observational window at ultra-low frequencies, enabling us to probe the lowest-energy cosmic rays—the bulk of the cosmic-ray population—for the first time. By combining LOFAR2.0 data and advanced computational methods with complementary higher-frequency radio observations, the project will deliver deep, high-resolution maps of galaxy clusters and study the physical processes responsible for cosmic-ray acceleration and filamentary radio structures.
  
  
• PhD project 6: Chemical abundances and the stellar initial mass function in massive quiescent galaxies over cosmic time
  Supervisor: Mariska Kriek
  Description: In recent years, it has become clear that massive galaxies formed and evolved much faster than predicted, with many already mature when the Universe was only a fraction of it current age. Yet we still lack a clear understanding of how these galaxies assembled so rapidly, and how massive they truly are. A PhD position is available in the group of Prof. Mariska Kriek to study the chemical abundances and stellar initial mass function of massive quiescent galaxies across cosmic time, primarily using data from the James Webb Space Telescope. The PhD candidate will analyse ultradeep spectroscopic data and contribute to the development of new tools and techniques for their interpretation. This research will provide new insight into the chemical enrichment and formation histories of massive galaxies, and help determine their true masses.
  
  
• PhD project 7: Resolving Galaxies over Cosmic Time
  Supervisor: Mariska Kriek
  Description: With the James Webb Space Telescope, it has become possible to study galaxies across cosmic time in unprecedented detail. Resolved spectroscopy and medium-band photometry now allow self-consistent analyses of galaxy structures and their stellar, gaseous, dusty, and metal content. A PhD position is available in the group of Prof. Mariska Kriek to explore these topics, primarily using JWST data. The candidate will contribute to the development of new tools and techniques for interpreting photometric and spectroscopic observations. This research will shed new light on dust–star geometries, the buildup of stellar mass, and the processes that eventually quench star formation.
  
  
• PhD project 8: Stellar Dynamics and Multi-Messenger Transients Around Supermassive Black Holes
  Supervisor: Elena Maria Rossi
  Description: Galactic nuclei are fascinating objects: the densest stellar systems in the universe, surrounding a supermassive black hole. They are the formation place of extreme electromagnetic and gravitational wave transients. This upcoming decay will see a wealth of observational data for the study of transients, from LSST/Rubin Observatory, ULTRASAT, and LIGO/VIRGO and LISA gravitational wave observatories. The student will work on the theory of how stars and black holes interact with each other, and with the massive black hole, and predict the observational consequences. In particular, two phenomena may be investigated in detail, according to the best match with the student: stars tidally disrupted by massive black holes, which give rise to flares that will appear abundant in LSST; the other gives rise to gravitational wave emission, and involves stellar mass black holes revolving around massive black holes (called Extreme Mass Ratio Inspirals), that will be prominent LISA sources. The PhD is mainly theoretical/computational with applications to data.
  
  
• PhD project 9: Salts: the secret catalyst of ice evolution on the path to biomolecules in planetary systems
  Supervisors: Melissa McClure and Ewine van Dishoeck
  Description: Life on Earth arose from a mixture of molecules with the elemental building blocks C, H, O, N, and S, which were delivered to our planet as solids, like ices and salts, during Earth's assembly. To understand the rise of life on Earth and the potential for life elsewhere, it is critical to trace the chemical evolution of ices from where they form in cold molecular clouds to where they are incorporated into planets within protoplanetary disks around young stars. Ammonium hydrosulfide salt was recently identified in interstellar ices based on JWST observations and laboratory experiments (https://www.astronomie.nl/nieuws/en/lost-sulfur-in-the-universe-found-in-salt-on-dust-and-pebbles-4349). Salt inclusions in interstellar ices may act as catalytic sites, as well as reactants in chemical pathways leading to the molecular building blocks of life. Additionally, they may provide reservoirs for key elements, especially N and S, during protostellar infall into the comet forming regions of protoplanetary disks.
  
  In this project, the student will use our access to JWST and ALMA protostar programs to track the formation and chemical evolution of salts from clouds to disks. The student will be embedded within several international observing collaborations. Their work will take place within a joint Danish-Dutch astrochemistry consortium, InterCat (https://phys.au.dk/intercat), in conjunction with one other local PhD student and several students and postdocs at the Aarhus and Copenhagen nodes. Locally, they would be situated within the astrochemical planet formation group at Leiden, with several other PhD students and postdocs working on diverse topics.