The first direct detection of gravitational waves opened the possibility of mapping the Universe via this new and independent messenger.

One of the most important correlation functions in physics, especially in cosmology, is the energy density, which describes how much energy is present at each point in spacetime due to matter fields. A key contribution to the energy density of the primordial universe comes from gravitational waves (GWs),…

We explored the Universe using weak gravitational lensing, a phenomenon that occurs when light from distant galaxies is bent by the gravitational fields of closer cosmic objects, much like how a lens distorts light.

Promotor: K. Kuijken, Co-Promotor: H. Hoekstra

In this work, I explore the creation of new methods that optimize simulations of the gravitational N-body problem. Specifically, I take advantage of the recent popularity of Machine Learning methods to find tools that can suit this problem.

Of all the mass in our Universe, 80% is thought to consist of a hypothetical and invisible substance called dark matter (DM).

In astronomy, the interpration of observations and measurements plays a crucial role: we rely purely and fundamentally on the information that reaches us as observers. And 80% of all matter in the universe is undetectable directly.

In this thesis we study the landscape of gravitational models which modify GR by introducing an additional scalar degree of freedom (d.o.f.) to source Cosmic Acceleration.

This thesis investigates the structural evolution and assembly of galaxies since the first few billions years after the big bang.

At the largest scales, two ingredients dictate the distribution of matter in the Universe. The first is dark matter, acting as an invisible scaffolding held together by gravitational forces.

For centuries astronomers studied the Universe by collecting light. Nowadays, we are living in times of great technological advancements, which allow us to explore our Universe in a new way - though gravitational wave radiation.

The physical origin of the dozens of stellar-mass binaries, the mergers of which have been detected by the LIGO-Virgo-KAGRA collaboration via gravitational waves, is still unknown.

Galaxy intrinsic alignments induce a major astrophysical contamination to weak gravitational lensing measurements and need to be modelled and mitigated when extracting cosmological information from such measurements.

The ultimate goal of cosmologists is to find a cosmological model able to explain the current observational data.

Promotor: Koen Kuijken Co-promotor: Henk Hoekstra

Galaxies form and live inside dark matter haloes. As a consequence, they are exposed to the tidal fields generated by the surrounding matter distribution: this imprints a preferential direction to the galaxy shapes, which leads to a coherent alignment on physically close galaxies, called intrinsic a…

In this thesis, the research focuses on the properties of dark matter and dark matter haloes and how they connect with the galaxies we can observe in the Universe.

Three major cosmology-focused missions are planned for the next decade: the Euclid space telescope, the Vera C. Rubin Observatory in Chile, and the Nancy Grace Roman Space Telescope.

Promotor: Prof.dr. J. Schaye, Co-promotor: Marcello Cacciato

What physics controls the properties of quantum matter, such as how electrons flow inside high-temperature superconductors? This question has captivated the physics community and industry for decades, in part due to the great technological potential such materials have, but also because they have resisted…

Improvements of weak gravitational lensing shape measurements are presented and some used for data analysis.

Valetudo, zo hebben de astronomen het nieuw ontdekte Jupitermaantje genoemd. Het is een weerbarstig exemplaar dat dwars tegen haar soortgenoten in beweegt. In de Volkskrant reageert Leidse astronoom Simon Portegies Zwart op de bijzondere ontdekking.

This thesis is dedicated to the exploration of the primordial dark ages: unknown physics during the earliest stages of the Universe’s expansion that have not yet been directly probed by observations. Cosmic inflation is a burst of exponential expansion of space after the “Big Bang”.

The focus of the dissertation

Promotor: Jelle S. Kaastra Co-promotor: Jelle de Plaa

There are many interpretations of quantum mechanics, and ultimately experiments are needed to verify or falsify these interpretations.

This thesis is a (biased) journey through very different topics in astrophysics: quasars and new populations of active galactic nuclei, gravitational waves from merging black holes, and protoplanetary discs around young stars.

The high velocity tail of the total velocity distribution of stars provides essential insight into fundamental properties of the Galaxy.

The radio sky harbours both galactic and extragalactic sources of arcminute- to degree-scale emission of various physical origins. To discover extragalactic diffuse emission in the Cosmic Web beyond galaxy clusters, one must image low–surface brightness structures amidst a sea of brighter compact fore-…

In samenwerking met Rijksmuseum Boerhaave, naar aanleiding van de tijdelijke tentoonstelling 'Dichter bij het zwarte gat', te zien t/m 5 januari 2025.

De meeste materie in het heelal is onzichtbaar, vermoeden veel astronomen. Maar hoe weeg je donkere materie die je niet kunt zien? Hoogleraar Henk Hoekstra zoekt naar een oplossing. Oratie op 25 juni.

De Leidse Sterrewacht gaat een nieuwe techniek gebruiken om te rekenen aan zwaartekrachtlenzen. Zij doen dit in het kader van onderzoek naar de vorming van melkwegstelsels. Alessandro Sonnenfeld van de Universiteit Tokyo haalde een Marie-Curie beurs binnen en komt het onderzoeksteam versterken.

Astronomen willen het heelal begrijpen, van de Oerknal tot nu, en hoe dit verder zal gaan. In Leiden concentreren ze zich daarbij op twee vragen: 'Hoe ontstaan sterren en planeten? en 'Hoe ontstonden in het jonge heelal sterrenstelsels en zwarte gaten?' Een nieuwe generatie telescopen – net klaar of…

Grenzen van quantum-theorieën verleggen, dat is precies waar de natuurkundigen van de Universiteit Leiden goed in zijn. Leidse onderzoekers starten acht nieuwe quantum-onderzoeksprojecten binnen het consortium Quantum Limits.

Het verzamelen en interpreteren van grote hoeveelheden data is niet meer weg te denken uit de maatschappij en de wetenschap. De Universiteit Leiden is een kennis- en expertisecentrum van data science dat de nadruk legt op interdisciplinaire samenwerking en innovatie.

Astronoom Henk Hoekstra is met ingang van 1 augustus benoemd tot hoogleraar Observationele kosmologie aan de Sterrewacht van de Universiteit Leiden.

Eeuwenlang hebben astronomen het heelal bestudeerd door lichtsignalen te verzamelen. Sinds 2015 stelt het bewijs van een belangrijke voorspelling van Einstein ons in staat om het heelal op een nieuwe manier te onderzoeken: door middel van zwaartekrachtgolven. Astronomie promovendus Valeriya Korol heeft…

Lezing, Astronomy on Tap

Lezing, Astronomy on Tap

Lezing, Oort lecture