Colloquia

One of the most fundamental questions in astronomy is how stars, the building blocks of the Universe, form. We generally understand that stars emerge from dense regions within molecular clouds, called prestellar cores, which collapse under gravity to form protostars, but many details of this process remain elusive. Despite significant advances in instrumentation and modelling, we still lack a complete understanding of how stars and planetary systems develop. A crucial piece of this puzzle lies in the protostellar phase, particularly the accretion process responsible for stellar mass growth at the early and more embedded stages of star formation. In this talk, I will review the current state of knowledge on accretion, presenting my work on last observational results of the early stages of star formation and discussing their implications for the broader star and planet formation scenario. 

Relativistic jets are amongst the most important and powerful phenomena in astrophysics, and yet also amongst the least understood. Most well known in the context of supermassive black holes in active galactic nuclei (AGN), relativistic jets are also the underlying mechanism behind gamma-ray bursts (GRBs) and LIGO neutron star merger afterglows, and a fundamental component of Tidal Disruption Events. Stellar mass (<20 solar masses) black holes and neutron stars in binary systems, known as 'X-ray binaries' (XRBs), are the local, lower-mass, and hence faster-evolving analogues to AGN, as well as being the direct descendants of GRBs and on the same mass scale as the LIGO merging BH. The near scale-independence of accretion and jet formation with BH mass, theoretically expected and observationally established, demonstrates that what we learn from XRBs can be applied to more massive systems such as AGN. In the past 6 years observations with the MeerKAT telescope have revolutionised our understanding of these jets, allowing unprecedented investigations into the power of black hole jets, measured as we track them decelerating and transferring their launch kinetic energy to the ambient ISM. These observations have also increased our sample size sufficiently that we can now make definitive statements about the relation between jet speed, jet precession, the nature of the compact object, and the connection to black hole spin.

Mathematics of atmospheric fronts: S.Q.G.(Surface Quasigeostrophic Equation) is a relevant model to understand the evolution of atmospheric fronts. It represents also a mathematical challenge, because of its non-linear and non-local character, which illustrates the rôle of mathematics in the development of science.

This colloquium will be held in person in the Aula

In the local universe most of the stellar mass is in passive galaxies, where star formation is
absent or at very low levels. Understanding what are the mechanisms that have been
responsible for quenching star formation in galaxies, and transforming them into passive,
quiescent systems, is one of the main observational and theoretical challenges of extragalactic
astrophysics. I will give a brief overview of the several possible quenching causes and physical
processes that have been proposed so far, ranging from feedback from black hole accretion and
starburst activity, to effects associated with the large scale environment in which galaxies live.
Although most of these mechanisms and causes play a role in different classes of galaxies and
at different epochs, multi-band observations are providing growing evidences that just a few of
them play the key, dominant role.
I will conclude by providing prospects for further investigating these aspects and tackling open
questions with the next generation of observing facilities.

Globular clusters (GCs) are fascinating objects nearly as old as the Universe that provide insight on a large variety of astrophysical and cosmological processes. However, their formation and their early and long-term evolution are far from being understood. In particular, the classical paradigm describing GCs as large systems of coeval stars formed out of chemically homogeneous material has been definitively swept away by recent high-precision spectroscopic and deep photometric observations. These data have provided undisputed evidence that GCs host multiple stellar populations, with very peculiar chemical properties. In this talk, I will review the properties of these multiple populations, before presenting the different scenarios that have been proposed to describe their formation. I will focus on the (many) current theoretical issues and open questions. 

This talk will address the preferred mass and time for galaxy formation, in dark-matter haloes similar to that of the Milky way but when the Universe was a few Gigayears old. It is proposed that this is due to the interplay between two mechanisms, first *supernova* feedback that removes gas from the galaxy, and second *hot gas* in the deep potential well of massive haloes that suppresses cold gas supply to the galaxy, the two being effective in galaxies of lower and higher masses respectively. Cosmological simulations reveal that the same mechanisms are responsible for a robust sequence of events were galaxies undergo a dramatic gaseous *compaction*, sometimes caused by mergers, into a compact star-forming “blue nugget”. This triggers inside-out *quenching* of star formation, which is maintained by a hot massive halo aided by black-hole feedback, leading to todays passive elliptical galaxies. The blue-nugget phase is responsible for drastic transitions in the main galaxy structural, kinematic and compositional properties. In particular, the growth of the *black hole* in the galaxy center, first suppressed by supernova feedback when below the critical mass, is boosted by the compaction event and keeps growing once the halo is massive enough to lock the supernova ejecta by its deep potential well and the hot halo. The compaction events also trigger the formation of extended rings in high-z massive galaxies. These events all occur near the same characteristic halo mass, giving rise to the highest efficiency of galaxy formation and black-hole growth at this magic mass and time.

Zoom link:  https://rediris.zoom.us/j/98813487304

Mindfulness o atención plena es un estado de la mente que permite estar atento al momento presente con aceptación. Y describe también la técnica psicológica que permite alcanzar este estado. Mindfulness se asocia a una gran bienestar físico y psicológico y por eso su práctica se está extendiendo a nivel internacional y se aplica en el área de la salud, la educación y las organizaciones.
En el coloquio sentaremos las bases teóricas de mindfulness, realizaremos algunas prácticas básicas y analizaremos los mecanismos de acción y la utilidad de mindfulness en el día a día.

We should find life beyond the solar system ("exolife") within a decade. This will require optical instruments that can perform exoplanet direct imaging.  There are good reasons to expect that telescopes from the ground will lead this search. Unfortunately, none of the currently envisioned large telescopes are optimal for detecting and measuring the emitted or reflected starlight from life-bearing exoplanets. This talk will describe what a 20-100m-class optical telescope would look like and could do if it were designed to solve exoplanet imaging problems. Such a telescope could be initiated today using technologies that are either currently available or under vigorous development.

Time-domain space missions have revolutionized our understanding of stellar physics and stellar populations. Virtually all evolved stars can be detected as oscillators in missions such as Kepler, K2, TESS and PLATO.  Asteroseismology, or the study of stellar oscillations, can be combined with spectroscopy to infer masses, radii and ages for very large samples of stars.  This asteroseismic data can also be used to train machine learning tools to infer ages for even larger stellar population studies, sampling a large fraction of the volume of the Milky Way galaxy. In this talk I demonstrate that asteroseismic radii are in excellent agreement with those inferred using Gaia and spectroscopic data; this demonstrates that the current asteroseismic data is precise and accurate at the 1-2% level.  Major new catalogs for Kepler and K2 data are nearing completion, and I present initial results from both. We find unexpected age patterns in stars though to be chemically old, illustrating the power of age information for Galactic archeology.  Prospects for future progress in the TESS era will also be discussed.