Colloquia

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.

Constraining dust optical properties is essential for interpreting remote sensing observations of planetary atmospheres and surfaces, as well as for understanding the radiative impact of aerosols in climate and circulation models. In this talk, I will present recent advances in the retrieval and experimental characterization of dust optical properties across the ultraviolet, visible, and near-infrared wavelengths. Our approach combines laboratory measurements with advanced light-scattering modeling to determine wavelength dependent complex refractive indices and other key parameters such as single-scattering albedos, cross sections, and efficiencies. Three Martian dust analogues were analyzed, each prepared with narrow particle size distributions representative of airborne dust in the Martian atmosphere. Particular attention was given to the effects of particle shape, composition, and size on the derived optical properties. The resulting validated optical property database covers wavelengths from 200 to 2000 nm and provides a physically consistent foundation for radiative transfer modeling. These results offer improved constraints for interpreting spacecraft and ground based observations of planetary materials and contribute to the broader understanding of dust scattering behavior in planetary environments.

The search for supermassive black hole binaries (SMBHBs) seemingly saw the dawn of exploration over the past twenty years with several hundred sub-pc candidates claimed from photometric and spectroscopic surveys monitoring active galactic nuclei (AGNs). While the existence of SMBH pairs have been detected at kpc separation, the observational evidence for sub-pc SMBHBs is however still inconclusive. Finding and
expanding the arsenal of SMBHB candidates is not only vital for understanding the co-evolution with their galactic hosts, but is complementary to pulsar timing arrays searching for low-frequency gravitational waves. With the advancements of upcoming high-precision, wide-field optical photometric surveys, like Vera Rubin’s LSST, robust electromagnetic detections may therefore happen in the near future.
Following the pursuit of confirming SMBHBs in the optical, we explore the possibility of using the ESA Plato space mission to detect the photometric signature of Doppler boosting and gravitational self-lensing events linked to their binarity. Although not designed for it, in this seminar we will discuss how Plato may play an essential role in future searches of SMBHBs and for AGN variability research in general. With a minimum 2-yr baseline per pointing field, our simulation study also serves as a benchmark for the upcoming Plato Guest Observer (GO) call in April 2026 designed for complementary sciences alike