Colloquia

The implementation of Adaptive Optics at the GTC, combined with the science instrument FRIDA -- an imager and integral field spectrograph operating in the near-infrared —- represents a factor of 10 to 15 improvement in angular resolution compared to current or planned GTC instruments. These resolutions are still a factor of 1.5 to 4 better than those achieved by the finest space telescopes, JWST and HST. This presentation highlights the imminent realisation of these capabilities at the GTC and the unique scientific opportunities enabled by the GTC+AO+FRIDA combination. To this end, I will outline possible science pathways that are uniquely possible with GTC+AO+FRIDA, ranging from stellar surface mapping to studies of the Local Group at the finest spatial scales and the high-redshift Universe.

The aim of this presentation is to introduce the research I have carried out in recent years, which led to being awarded a Ramón y Cajal fellowship, and to outline the future goals of the project. I will cover the three main pillars of my work: the analysis of spectropolarimetric observations, the use and development of inversion codes (computational tools used to infer the physical parameters of the solar atmosphere from these observations), and the design of state-of-the-art instrumentation for ground-based, balloon-borne, and space telescopes. All of these efforts serve a common purpose: advancing our understanding of the Sun. Thus, I will also touch on some of the most compelling open questions in solar physics I have worked on, including the nature of quiet Sun magnetism and the energy release mechanisms behind solar flares.

 The fate of massive stars and the type of supernova (SN) they produce are closely linked to their final stages of evolution. During these late phases, stars may undergo episodic mass loss, forming circumstellar material (CSM) that can leave observable signatures in the SN spectra, particularly as resonance lines in the near-ultraviolet (NUV). In this talk, I will present a sample of superluminous supernovae (SLSNe), an exceptionally luminous class of SNe, focusing on the NUV spectroscopy to search for signatures of recently ejected CSM shells. I will first discuss two SLSNe in which CSM shells are detected, inferring their properties and the timing of the ejection, along with implications for the underlying mass-loss mechanisms and progenitor systems. I will then extend the analysis to the full sample, modelling the spectral regions where CSM-related features are expected in order to evaluate how common such mass-loss episodes are and to place constraints on undetected CSM shells. These results provide new insights into the final stages of massive star evolution and help constrain the nature of SLSN progenitors.

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.