Events, Seminars, Talks

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To arrange a visit with the speaker during the visit, please contact their host: Anna de Graaff

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The WST project aims to design and construct an innovative 10-metre class wide-field spectroscopic survey telescope (WST) in the southern hemisphere. It will feature the parallel operation of two cutting-edge instruments: a high-multiplex (32,000), large field-of-view (3 square degrees) multi-object spectrograph (MOS) operating in both low- and high-resolution modes, and a giant panoramic integral field spectrograph (IFS). WST’s ambitious top-level requirements place it well ahead of all existing and planned facilities. In its first five years of operation, the MOS is expected to observe 300 million galaxies, 25 million stars at low resolution, and 2 million stars at high resolution, while the IFS will deliver 4 billion spectra. These capabilities will enable transformative science across a wide range of astrophysical domains. A key strength of WST lies in the synergy between its MOS and IFS instruments, offering highly complementary spectroscopic survey modes. This dual approach is central to the project’s scientific ambition. WST is envisioned as the next major facility for ESO following the ELT, and a proposal will be submitted in response to the upcoming ESO Call for Ideas in 2027. The project is backed by a large consortium of leading institutes from European countries and Australia, with deep expertise in astronomical instrumentation and survey science. To arrange a visit with the speaker during the visit, please contact their host: Dylan Nelson

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The PHANGS-HST and JWST Treasury Programs have produced the most extensive inventories to date of optically visible and dust-obscured star clusters across nearby galaxies. A coherent picture is emerging of the earliest phases of star formation, built from complementary studies that consistently point to short dust-clearing timescales (~3 Myr), in agreement with earlier optical studies. Together, these results underscore the central role of early, pre-supernova feedback in regulating the star formation cycle. Drawing on the statistical power of tens of thousands of clusters spanning dozens of galaxies, I will synthesize what PHANGS and related programs have revealed about cluster evolution, feedback, and the use of clusters as “clocks” for timing key phases of star formation. Looking ahead, I will highlight work on the Habitable Worlds Observatory, NASA’s next flagship astrophysics mission after Roman, which will operate as a true “Super-Hubble,” with UV–optical capabilities to transform our understanding of star formation and fields across astrophysics. To arrange a visit with the speaker during the visit, please contact their host: Ralf Klessen

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The common envelope interaction happens between a growing or giant star of any mass and a more compact companion. The compact objects inspirals in the outer layers of the large star fully ejecting the envelope or merging with the core. The CE interaction is at the origin of a number of single and binary objects such as the progenitors of Type Ia supernovae, cataclysmic variables or the hypothesised Thorne-Zytkow objects. While 3D hydro simulations have come a long way in the last decade, observations of this fast phase have lagged, until recently. Time-resolved surveys have recently observed a number of objects that today are grouped into a single (albeit somewhat diverse) class called Luminous Red Novae. These have been identified as common envelope mergers and marrying these observations with simulations has become a priority to explain the observations and to (finally!) constrain the simulations. I will present the first simulations that target directly LRN light curves also including the effects of dust nucleation, essential to reproduce light and colours of these objects. To arrange a visit with the speaker during the visit, please contact their host: Fritz Röpke

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Strongly lensed supernovae (SNe) are emerging as a new probe of cosmology and SNe. When a SN is strongly lensed by a foreground galaxy, multiple images of the SN will appear around the foreground galaxy at different times. Current surveys including Euclid and the Rubin Observatory Legacy Survey of Space and Time will capture hundreds of strongly lensed SNe, expanding the existing sample by two orders of magnitude. These events offer excellent opportunities to: (1) measure the Hubble constant via lensing time delays, shedding light on the Hubble tension, and (2) obtain unprecedented constraints on SN progenitors through early-phase spectra. I will give an overview of the first discoveries of lensed SNe and their cosmological implications. To arrange a visit with the speaker during the visit, please contact their host: Philipp Girichidis

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Galaxies do not grow in isolation, but within a cosmic web of intergalactic gas. The evolution of the galaxies and this intergalactic medium are closely connected. As the first galaxies formed, their light heated the gas surrounding them in a process known as reionization. Measuring the progress of reionization can give us an indirect view of how and when the first galaxies formed, complementary to direct observations of the galaxies themselves with telescopes like JWST. In this talk, I will discuss how we can constrain the timing of reionization with different observational probes, such as absorption in the spectra of distant luminous objects. I will present my work interpreting these observations with large cosmological simulations of the intergalactic medium. I will discuss what is known about the history of reionization, and what questions are still to be answered. To arrange a visit with the speaker during the visit, please contact their host: Sarah Bosman

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Theories of galaxy formation, structure, and evolution increasingly include the effects of cosmic rays on gas dynamics and energy balance. This is usually done by treating the cosmic rays as a fluid that is coupled to the thermal gas by magnetic fields on global scales and electromagnetic fluctuations on kinetic scales. I will discuss the foundations and assumptions of the fluid model, assess whether it is correct and complete, where it can be improved, and how it can be tested. To arrange a visit with the speaker during the visit, please contact their host: Max Gronke

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To arrange a visit with the speaker during the visit, please contact their host: Max Gronke

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In recent years, cosmic rays (CRs) have emerged as a key factor shaping the interstellar medium (ISM) properties and influencing galaxy evolution. Yet, despite significant advances, modelling CR transport on galactic scales remains challenging, largely due to the complex microphysical interactions between CRs and thermal gas. As a result, the true extent of CR impact on ISM structure and evolution is still uncertain. In this talk, I will present our latest efforts to model CR transport within the TIGRESS MHD simulations of the multiphase ISM. I will discuss how CRs affect the dynamical and thermal state of the ISM in Milky Way-like galaxies, showing that while they have little effect on the star formation rate in galactic disks, they significantly accelerate warm outflowing gas with mass loading factors higher than in simulations without CRs. These results hold across different galactic environments. Beyond these theoretical insights, some simulations include a spectral treatment of CR protons and electrons, allowing us to construct synthetic observables - such as CR spectra and non-thermal emission - for direct comparison with observations. I will present our initial results comparing synthetic CR spectra with measurements in the solar neighbourhood, highlighting a very good agreement, and discuss the implications for CR transport. To arrange a visit with the speaker during the visit, please contact their host: Philipp Girichidis

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To arrange a visit with the speaker during the visit, please contact their host: Michela Mapelli

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Shock waves are the universe's most prolific particle accelerators. The same mechanism, diffusive shock acceleration, is invoked to explain energetic particles in the solar wind, cosmic rays from supernova remnants, and relativistic electrons at merger shocks in galaxy clusters. In this picture, particles gain energy by repeatedly scattering back and forth across the shock front, aided by turbulent magnetic fields. Turbulence, however, does not have to produce ordinary diffusion. If particles occasionally make very long, uninterrupted excursions, they spread much faster than a random walk allows. This behaviour, known as a Lévy walk or superdiffusion, appears in systems ranging from wild fires to particles transport in the heliosphere. Radio relics are arcs of synchrotron emission that can extend over megaparsecs, tracing shocks driven by colliding galaxy clusters. They provide a natural laboratory for testing how particles are transported on large scales. We discovered that several relics show faint radio emission reaching up to 100 kpc ahead of the shock, where standard theory predicts almost nothing. I will show that superdiffusive electron transport explains this precursor naturally. I will then discuss how the spectral index profile ahead of the shock, measurable with LOFAR, MeerKAT and soon the SKA, can distinguish true superdiffusion from simply faster normal diffusion. In the final part, I will show what other curiosities recent radio observations have revealed about cosmic-ray transport in the intra-cluster and intra-group medium. To arrange a visit with the speaker during the visit, please contact their host: Max Gronke

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