Colloquia

Supernovae are usually cast as efficient dust destroyers. I will show that, when realistic environments are taken into account, they instead emerge as net dust enrichers. Combining 3-D hydrodynamic simulations with semi-analytic cooling and cloud-crushing calculations, I follow dust processing from ejecta and wind-blown bubbles to dense circumstellar shells, dusty clumps, and sequential supernovae in compact star clusters. Across these environments, rapid radiative cooling often limits dust destruction, and in dense shocked clumps can even open a path to further growth. The result is a consistent picture in which supernovae inject and build up dust in remnants, superbubbles, and star-forming clouds. On cluster scales, the key question then becomes retention: how much of that dust remains in the system, and how much is vented out by clustered explosions. This may help explain both the low retained dust content inferred for Blue Monsters at z>10 and the emergence of dustier systems by z≤8, all within the first few hundred million years of cosmic time.

We are delighted to welcome F. Duncan Haldane, winner of the Nobel Prize in Physics, for a very special seminar.

The study of “topological states” in quantum condensed matter has been very active in recent years. Though it was initially discovered over 45 years ago, the quantum Hall effect continues to reveal new surprises and is at the heart of quantum topology, expecially in its “fractional” presentation.

*After the colloquium, a science coffee will be served in the cafeteria.

Exactly a hundred years ago, in January 1926, Schrödinger established the famous equation bearing his name which  marked the birth of quantum physics. Among all the inventions born of this physics, the laser occupies an important place, both for the rich history of discoveries that led to its birth, and for the role it plays today in fundamental and applied research. This history began at the time of the “old quantum theory” with Einstein's discovery of stimulated emission in 1916 and Stern's discovery of the spatial quantization of the atomic angular momentum in 1922. Nuclear magnetic resonance (1945), optical pumping (1952), atomic clocks and the maser (1954) followed, leading in 1960 to the invention of the laser. This extraordinary light source plays an essential role in many modern technologies. It has also opened up fields of research in blue sky science that could not have been imagined at the time of its birth. We owe to it the cooling and trapping of atoms, the study of quantum gases of bosons and fermions, the discovery of gravitational waves and the manipulation of individual quantum particles, which has led to current research into quantum simulation and quantum computing. The laser may also provide answers to fundamental questions about the link between quantum physics and gravitation, or about the nature of the hypothetical dark matter. The rich history of the laser is a vivid illustration of the close link between fundamental research and technology.

In this talk, one of the authors of The Reinvention of Science. Slaying the Dragons of Dogma and Ignorance explores how science has often relied on postulated but unseen entities to explain observations. Historical examples include phlogiston, the luminiferous ether, the homunculus, and crystalline spheres. Some such entities hindered progress, while others were later confirmed. Neptune exemplifies a successful prediction later observed, whereas the hypothetical planet Vulcan was discarded after Einstein’s general relativity explained Mercury’s orbit. Today, cosmology invokes Dark Matter and Dark Energy: will they prove to be “Neptunes” or “Vulcans”?

The second part examines an ongoing paradigm shift concerning the end-Cretaceous mass extinction 66 million years ago. The dominant view attributes dinosaur extinction to a Yucatán asteroid impact, a conclusion widely accepted in science and popular culture. However, research led by Princeton paleontologist Gerta Keller suggests extreme volcanism in India’s Deccan Traps began at least 400,000 years before the impact and had already driven widespread ecological decline. The asteroid certainly impacted, but may have been neither necessary nor sufficient to cause the extinction. Despite this evidence, the impact hypothesis still dominates public understanding, while alternative models incorporating prolonged volcanism continue to develop.

The ESO Extremely Large Telescope project is in the final stages of AIV. The bulk of the telescope and dome are erected on site and almost half the primary mirror segments are already in Chile. The rest of the optics are well advanced as are the wavefront sensing capabilities. The talk will present the current status of the hardware and software systems and discuss the issues arising from thinking about, designing, and building the telescope.

Understanding the origin of the elements remains one of the major challenges of modern astrophysics. Ultraviolet (UV) spectroscopy of metal-poor stars provides access to many absorption lines of elements and species that are otherwise undetectable in optical or infrared spectra. I will show how UV spectra collected with the Hubble Space Telescope have expanded stellar chemical inventories to more than 65 elements per star, identified signatures associated with r-process transuranic fission fragments, and provided new calibrations for NLTE radiative transfer calculations. I will also show how UV spectroscopy with the ANDES instrument on the Extremely Large Telescope and the proposed Habitable Worlds Observatory mission could revolutionize our understanding of the first stars in the decades ahead.

In this talk, I will explore the possibility that some of the most salient challenges of galaxy formation might have a fundamental origin, rather than simply indicate a problem in our understanding of the modeling of baryons within the LambdaCDM cosmological model. I will thus present how alternatives to cold dark matter can help (or not) to solve some of these riddles, going all the way from warm, mixed, fuzzy or self-interacting dark matter to more radical alternatives such as modified gravity.

The massive globular cluster Omega Centauri is likely the stripped nucleus of an accreted dwarf galaxy and, therefore, provides a unique opportunity to study the central region of a galaxy, whose evolution halted billions of years ago.

In the last years we have created oMEGACat, the largest astrometric and spectroscopic dataset for any star cluster, with the goal to decipher both the formation history and the dynamics of Omega Centauri.

I will give an overview of this project and then focus on the exciting discovery of several fast-moving stars in the very center of the cluster. These stars provide the potentially best evidence for an intermediate-mass black hole (IMBH) we have to date.

 These elusive IMBHs have masses between the stellar mass black holes and supermassive black holes and may provide a missing link in our understanding of the formation of super-massive black holes

Massive stars are the cosmic engines of the universe, driving the chemical enrichment and mechanical evolution of galaxies. A large fraction of massive stars are found in binary systems, and interactions between these stars can fundamentally alter the evolutionary paths of both stars. One of the most critical phases in the evolution of massive binary stars is the contact phase, where both stars fill their Roche lobes and share a common envelope. The contact phase represents a crossroad in the evolution of massive binary stars.  Depending on the internal physics, the predicted end products can vary greatly including various exotic objects such as Be stars, magnetic massive stars, LBVs, peculiar Type-II supernovae, and gravitational wave sources. Nearly a quarter of all massive stars will evolve through a contact phase at some point during their lifetimes, however, despite its importance, large uncertainties exist in our understanding of the internal physics and the final evolutionary outcome of this phase. This is due to both the complex interaction physics and a lack of observational constraints: only 13 massive contact binaries are currently known.

Despite the small sample size, massive contact binaries can provide vital observational constraints to the various evolutionary pathways that involve binary mergers. In this talk, I will discuss the current state of the field of massive overcontact binaries, with a specific focus on the internal mixing processes during this phase.  I will discuss the theoretical predictions as well as what the observational data tells us, and how these compare and contrast with one another.  I will also describe a new spectroscopic analysis technique specifically designed to analyze these highly deformed systems and I will discuss how accounting for the 3D geometry can change our understanding of these objects. Finally I will discuss the future direction of the field and how we can attempt to bridge the gap between theory and observations in the coming years.

Interacting binary evolutionary products are ubiquitous in cluster environments. This talk presents an overview of recent observational progress on blue stragglers and related post-interaction systems, including blue lurkers, yellow stragglers, and extremely low-mass white dwarfs. These objects trace alternative evolutionary pathways and occupy regions of the Hertzsprung–Russell diagram that are inaccessible to single stars, reflecting a diversity of mass-transfer histories and evolutionary states in cluster environments. Multiwavelength observations, particularly in the ultraviolet, have proven to be powerful tools for identifying compact companions and constraining the present-day binarity and origins of these systems. In combination, time-series photometry and spectroscopic follow-up provide the most direct means of measuring their fundamental parameters and extending insights from cluster populations to analogous systems in the field.