Program 2021

Tuesday 2nd February 2021 - Aula Conversi 16:30 - 17:30

"The astrochemical trail of our origin"

Cecilia Ceccarelli, Université Grenoble Alpes, IPAG

The Solar System was born 4.5 billions years ago, after a complex process whose details are not fully understood. The large number of detected extrasolar planets tells us that they are a common product of the star formation process, their variety that there are many ways of building them. How can then we recover the path followed by the Solar System?

Understanding the Solar-type star formation process currently taking place in the Milky Way is mandatory to answer this question. Astrochemistry, the science of how atoms and molecules combine  and evolve in the interstellar medium, is a powerful diagnostics to follow the evolution that turns a molecular cloud dense clump into a planetary system. But it can only be exploited once we know how to interpret the chemistry occurring in the exotic conditions of the interstellar medium, where quantum chemical effects dominate.

In this presentation, I will provide an overview of the major progresses of our understanding in astrochemistry and, more specifically, the one involved in the Solar System formation history.

Tuesday 23rd February 2021 - Aula Conversi 16:30 - 17:30

"Gamma ray Astronomy: the cross-road between Physics and Astrophysics"

Razmik Mirzoyan, Max Planck Institute for Physics, Munich, Germany

Thirty-two years ago a report about the measurement of unusual, so-called teraelectronvolt signal from the Crab Nebula captured the attention of the world scientific community. The authors reported a flux of so-called gamma-ray photons, where each carried an incredible amount of energy, exceeding that of the well-known X-rays by billion times. How and in which processes the nature managed to pack such a huge energy content into single photons remained a mystery for the coming years. Researchers used for observations a special technique and instrumentation dubbed as imaging atmospheric Cherenkov telescopes. In the following couple of years not much has happened and the community started speculating about the new science of a single source. More researchers joined that effort and already ten years after the initial discovery ~10 sources of teraelectronvolt gamma-rays were known. Today this discipline boasts to know more than 200 sources of very different origin, from supernova remnants to pulsars, from supermassive active galactic nuclei with black holes in their centre to gamma-ray busts, from binary systems to pulsar wind nebulae. A new discipline, the so-called astro-particle physics with diverse instrumentation appeared in the cross-roads between physics and astrophysics. In this lecture we will have a closer look to the details of this rapidly evolving, fascinating frontier science.

Tuesday 9th March 2021 - Aula Conversi 16:30 - 17:30

"Exploring cosmic reionization with 21cm telescopes"

Benedetta Ciardi, Max Planck Institute for Astrophysics

Cosmic reionization is the last major phase transition undergone by our Universe. Although most studies agree on the general characteristics of H reionization (for example that it is driven by stars and it is mostly if not fully complete by z~6), its details are still largely unknown, among which the contribution from and role played by more energetic sources.

In this talk I will discuss the ingredients needed for a correct modeling of cosmic reionization and present results from recent radiative transfer simulations accounting for a variety of source types (such as stars, quasars, X-ray binaries). I will then discuss the observability of reionization in terms of various diagnostics associated to the 21cm signal from neutral hydrogen and present the latest results from the LOFAR radio telescope.

Friday 16th April 2021 - Aula Conversi 16:30 - 17:30

"The future of cosmology"

Joseph Silk, Institut d’Astrophysique de Paris, The Johns Hopkins University, University of Oxford

One of the greatest challenges in cosmology is understanding the origin of the structure of the universe. The cosmic microwave background and large-scale surveys of galaxies have provided unique windows for probing cosmology and its inflationary origin. But where do we go next? Future experiments are planned with the next generation of observatories that will increase the current precision of cosmological measurements by an order of magnitude. However we need to do far better if there is to be a guaranteed science return that will definitively probe our cosmic origins. I shall argue that the ultimate goal for our future strategy must be astronomy from lunar-based telescopes.

Tuesday 18th May 2021 - Aula Conversi 16:30 - 17:30

"Quenching star formation in galaxies"

Roberto Maiolino, Cavendish Laboratory, University of Cambridge, UK

In the local universe stars only make up about 7% of all baryons, indicating that star formation has been extremely inefficient across the cosmic epochs. Within this context, even more impressive is the fact that in a significant fraction of galaxies star formation has been totally “quenched”, resulting into the population of passive and quiescent local galaxies. Understanding what are the mechanisms responsible for suppressing or even quenching star formation in galaxies has been one of the main challenges of astrophysics in recent years and it is one of the research areas in which most of the efforts have been directed, both in terms of cosmological simulations and in terms of observing campaigns.

I will give an overview of the potential causes and physical processes that might be responsible for regulating or even leading to the complete suppression of star formation in galaxies. I will illustrate that there are a variety of possible culprits. Among these I will show that supernova explosions can play a role, but the energy injected in the insterstellar and intergalactic medium by accreting supermassive black holes can have a truly dramatic effect on their host galaxies. The environment in which galaxies live (e.g. galaxy groups or clusters) can also play an important role, by suppressing star formation especially in satellite galaxies. I will discuss observational evidence for these various effects by using results from extensive multi-wavelength datasets.

I will conclude by emphasizing open, outstanding problems and the possibility of tackling them with the next generation of observing facilities.

Tuesday 1st June 2021 - Aula Conversi 16:30 - 17:30

"The evolution of massive black holes through cosmic times"

Debora Sijacki, Institute of Astronomy, University of Cambridge, UK

In this talk I will review current theoretical efforts in understanding supermassive black hole formation, accretion and feedback throughout cosmic time. Specifically, I will discuss possible links between large scale cosmological environments and supermassive black hole assembly and outline several possible interaction channels between active black holes and their host galaxies. In the second part of the talk I will focus on novel computational methods that allow us to follow black hole physics on much smaller scales in full galaxy formation simulations to unravel how black hole mass and spin evolve during the binary hardening stages or during launching of powerful jets.

Tuesday 22nd June 2021 - Aula Conversi 16:30 - 17:30

"The dark and luminous side of structure formation"

Piero Madau, Department of Astronomy and Astrophysics, University of California Santa Cruz

The beaded filamentary network of intergalactic gas in which galaxies form and evolve,  and which gives origin to a “forest”  of hydrogen Lyman-alpha absorption lines in the spectra of distant quasars, encodes information on the physics of structure formation, the nature of the dark matter,  the temperature and ionization state of baryons in the Universe. The potential of the Lyman-alpha forest for constraining with percent accuracy the matter density distribution on medium to small cosmological scales has motivated the construction of the Dark Energy Spectroscopic Instrument (DESI), which will measure absorption line spectra backlit by nearly a million high-redshift (z >2) quasars. In this talk I will describe the multiple steps needed to connect flux fluctuations in quasar spectra to physical parameters, present an unprecedented suite of  hundreds of  high-resolution hydrodynamical simulations of structure formation with different  thermal histories, and use it to perform a statistical comparison of mock spectra with the observed 1D flux power spectrum and other data. A likelihood analysis shows that, over the last 13 billion years,  gas in the cosmic web experienced four main heating and cooling epochs.

Tuesday 28th September 2021 - Aula Conversi 16:30 - 17:30

"Star formation through space and time"

Ralf Klessen, Institute for Theoretical Astrophysics, University of Heidelberg

Stars and star clusters are the fundamental visible building blocks of galaxies at present days as well as in the early universe. They form by gravitational collapse in regions of high density in the complex multi-phase interstellar medium. The process of stellar birth is controlled by the intricate interplay between the self-gravity of the star-forming gas and various opposing agents, such as supersonic turbulence, magnetic fields, radiative feedback, gas pressure, and cosmic rays. Turbulence plays a dual role. On global scales it provides support, while at the same time it can promote local collapse. This process is modified by the thermodynamic response of the gas, which is determined by the balance between various heating and cooling processes, which in turn depend on the chemical composition of the material. In this talk I will try to give an overview of the our understanding of the star-formation process, discuss some examples of the recent progress in the field, and speculate about the implications for stellar birth in the high-redshift universe.

Thursday 21th October 2021 - remote connection 16:30 - 17:30

"The appearance of very high red-shift quasars and the formation of super massive black holes "

Pavel Kroupa, University of Bonn and Charles University of Prague

Quasars are found to appear a few hundred Myr after the Big Bang, but pressing matter together into super-massive black holes (SMBHs) so quickly appears to be impossible. At a later stage, the spheroidal component of a galaxy (its bulge if it is not an elliptical galaxy) is observed to show a correlation between its mass and that of the central SMBH it harbours, although spheroids with a mass lower than a few 1E9 Msun appear to only host a nuclear star cluster. I will discuss a theory for the formation of SMBHs which accounts for these observations using standard, non-exotic physics. 

Tuesday 16th November 2021 - Aula Conversi 16:30 - 17:30

"Galactic planetary science"

Giovanna Tinetti, Department of Physics and Astronomy, University College London

Thousands of planets orbiting stars other than our own are being discovered (extrasolar planets). Since their discovery in the 1990s this field of astronomy and planetary science has exploded, being today one of the most exciting and dynamic. Even within the limits of our current observational capabilities, studies of extrasolar planets have provided a unique contribution to improving our view of the place that the Solar System and the Earth occupy in the galactic context. The arrival of more performing and dedicated facilities from space and the ground in the coming decade, will provide an unprecedented opportunity to study these worlds in great detail. In this talk, I will review highlights and pitfalls of our current knowledge of this topic and discuss the scientific and technical steps to be taken in this fascinating journey of remote exploration of the planets in our Galaxy.

Tuesday 14th December 2021 - Aula Conversi 16:30 - 17:30

The "unreasonable effectiveness" of the LCDM model

Licia Verde, ICREA and Institute of Cosmological Sciences, University of Barcelona

The standard cosmological model (the LCDM model) has been established and its parameters are now measured with unprecedented precision. 

This model  successfully describes observations from widely different epochs of the Universe, from the first few minutes, all the way to the present day. 

However, there is a big difference between modelling and understanding. The next decade  will see the era of large surveys; a large coordinated effort of the scientific community in the field  is on-going to map the cosmos producing an  exponentially growing amount of data. 

But precision is not enough: accuracy is also crucial.  The "unreasonable effectiveness”  of the LCDM model offers challenges and opportunities. 

I will present some of the lines of enquiry explored by my group in this direction.