PhD defence
From a Biased Perspective: Quasars, Mergers, and Planet-Forming Discs
- E. Pizzati
- Date
- Wednesday 29 October 2025
- Time
- Location
-
Academy Building
Rapenburg 73
2311 GJ Leiden
Supervisor(s)
Summary
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 the planet-forming discs around young stars.
Quasars, powered by supermassive black holes, shine so brightly that they can be seen across billions of light-years. By studying how quasars cluster together, I show that their distribution reflects the dark matter haloes they inhabit and reveals how rapidly black holes were growing when the Universe was young. Studying new observations from the James Webb Space Telescope, I also investigated mysterious compact sources nicknamed “little red dots.” They outnumber quasars by a wide margin and cluster like ordinary galaxies, suggesting they may represent a new phase of black hole growth—or perhaps something else entirely.
The thesis then moves into two other frontiers. Future gravitational wave detectors will be sensitive enough to pick up so many black hole and neutron star mergers that their signals may sometimes overlap. I explore how this complicates our ability to measure their properties and suggest ways to disentangle the signals. Finally, I return closer to home, to the discs of gas and dust around young stars—the birthplaces of planets. Using ALMA observations, I find that these discs are surprisingly calm, with dust confined to thin layers, hinting at low turbulence during planet formation.
Together, these studies show how connecting theoretical models with observations can sharpen our picture of the Universe—and sometimes force us to rethink what we thought we knew.
PhD dissertations
Approximately one week after the defence, PhD dissertations by Leiden PhD students are available digitally through the Leiden Repository, that offers free access to these PhD dissertations. Please note that in some cases a dissertation may be under embargo temporarily and access to its full-text version will only be granted later.
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