The latest puzzle in narrow-line Seyfert 1 galaxies: invisible jets?

Main Colloquium
Dr. Marco Berton
European Southern Observatory, Santiago, Chile

Narrow-line Seyfert 1 (NLS1) galaxies are a subclass of active galactic nuclei (AGN) identified more than 30 years ago, but still not entirely understood. These objects are likely characterized by rapidly growing low-mass black holes. Interestingly enough, some of them have been detected in gamma-rays, a sign that they can harbor powerful relativistic jets. In my talk I will review their properties, showing how the true nature of NLS1s is that of early-stage AGN in a recently triggered activity phase, and how they are connected to other classes of kinematically young jetted AGN. I will also report on the discovery, in a handful of NLS1s, of relativistic jets remarkably faint at low radio frequency, but extremely bright and variable at high radio frequency. New observations of these sources are revealing an increasingly complicated picture, and I will outline the different scenarios we are developing to explain this new, unexpected phenomenon.

The Renaissance of Astrophysics: a landscape of opportunities in the era of Time Domain Multi-Messenger investigations

Special Colloquium
Prof. Raffaella Margutti
Northwestern University, Evanston, Illinois, USA

Astronomical transients are signposts of catastrophic events in space, including the most extreme stellar deaths, stellar tidal disruptions by supermassive black holes, and mergers of compact objects. Thanks to new and improved observational facilities we can now sample the night sky with unprecedented temporal cadence and sensitivity across the electromagnetic spectrum and beyond. This effort has led to the discovery of new types of astronomical transients, revolutionized our understanding of phenomena that we thought we already knew, and enabled the first insights into the physics of neutron star mergers with gravitational waves and light. In this talk I will review some very recent developments that resulted from our capability to acquire a truly panchromatic view of transient astrophysical phenomena. I will focus on two key areas of ignorance in the field: (i) What are the progenitors of stellar explosions and what happens in the last centuries before death? (ii) What is the nature of the compact objects produced by these explosions and what happens when compact objects merge? The unique combination of Discovery Power (guaranteed by planned transient surveys across the electromagnetic spectrum, combined with efforts in the realm of artificial intelligence) and Understanding (enabled by multi-messenger observations) is what positions time-domain astrophysics for major advances in the near future.

A shocking shift in paradigm for classical novae

Main Colloquium
Prof. Laura Chomiuk
Michigan State University, USA

Over the last decade, our understanding of classical novae has been turned on its head with the discovery of gamma-rays from Galactic eruptions. This discovery has highlighted the value of novae -- non-terminal, thermonuclear eruptions on the surfaces of white dwarfs in binary systems -- as laboratories for studying shocks and particle acceleration. I will discuss where and how shocks form in the nova ejecta, why we think the shocks may actually dominate the energy budget of the nova eruption, and some of the consequences of the shocks, including dust formation and acceleration of particles to very high (TeV) energies. These recent developments place novae amongst the ranks of interaction-powered transients, making them nearby, common examples of the physics that governs more exotic events like Type IIn supernovae, stellar mergers, and tidal disruption events.

The Galactic centre: structure, dynamics and star formation of a unique astrophysical target

Main Colloquium
Dr. Mattia Sormani
Universität Heidelberg

I will give an introduction to the structure, dynamics and star formation in the centre of the Milky Way. After reviewing the basic theoretical tools, I will discuss several topics including (i) how can we interpret large-scale spectral line datacubes of CO, HI and other interstellar gas tracers in the context of gas flowing in the strongly non-axisymmetric gravitational potential of the Galactic bar; (ii) how can we use the gas dynamics to constrain the properties of the Galactic bar; (iii) what physical processes transport the gas inwards from the Galactic disc (R~3 kpc) to the Central Molecular Zone (CMZ, R~120 pc) and then to the central black hole SgrA*; (iv) what is the spatial and temporal distribution of star formation in the Galactic centre; (v) what are the structure, dynamics and secular evolution of the Nuclear Stellar Disc, the flattened stellar structure that dominates the gravitational potential at Galactocentric radii R between 30 pc and 300 pc. Finally, I will highlight some open questions and directions of future research.