Unless otherwise noted, the Astrophysics Seminars take place on Monday, usually every other week, at 1:30pm in Aula Caldirola.
November 2024
November 4th
Speaker: Davide Bianchi (Università degli Studi di Milano)
Title: Measuring our expanding Universe: one year of DESI observations
Abstract:
In its first year of observations the Dark Energy Spectroscopic Instrument (DESI) has built the largest map of galaxy redshifts to date, spanning the nearby universe to 11 billion light years. Accurate measurements of how galaxies distribute and cluster within this map allow us to trace the expansion history of the Universe to unprecedented precision and understand what role dark energy played in such process. In this talk I will present the first set of DESI cosmological results, coming from measurements of the baryonic acoustic oscillations (BAO) characteristic scale. (In the unlikely event that the results from “full shape” analysis will be released by the date of the talk I will include them in the presentation).
November 18th –> moved to November 25th
Speaker: Marion Villenave (Università degli Studi di Milano)
Title: Observational constraints on dust concentration and planetesimal formation in protoplanetary disks
Abstract:
To form giant planets during protoplanetary disk lifetime, small micron sized particles must grow rapidly to larger grains. A full understanding of that process requires a detailed characterization of the radial and vertical structure of the gas-rich disks associated with young pre-main sequence stars. This is because the level of dust concentration controls grain growth efficiency and planetesimal formation. Multi-wavelengths observations of protoplanetary disks, for example in the millimeter and near-infrared, allow to probe very different grain sizes that are differently affected by evolutionary mechanisms. Here, I will discuss observational constraints on dust accumulation in early and evolved disks, with a particular focus on recent constraints on vertical dust concentration using multi-wavelength observations from various instruments, such as ALMA, JWST, HST… The modeling of multi-wavelength observations of inclined disks allows to identify high density regions, favorable for grain growth and planet formation, and to study the efficiency of planet formation in protoplanetary disks.
December 2024
December 2nd
Speaker: Mattia Sormani (Università degli Studi dell’Insubria)
Title: The formation of nuclear rings in barred galaxies
Abstract:
I will give an introduction to our theory for the formation of nuclear rings, which are remarkable gaseous structures commonly found at the centre of barred galaxies including our own Milky Way. The rotating external bar potential excites strong density waves near the inner Lindblad Resonance. The density waves remove angular momentum from the gas disc and transport the gas inwards. The accumulation of gas at the inner edge of the gap is the nuclear ring. The process has many similarities with the opening of gaps in protoplanetary disks driven by embedded planets & with the opening of gaps in planetary rings driven by satellites.
December 16th
Speaker: Michele Moresco (Alma Mater Studiorum – Università di Bologna)
Title: Cosmology beyond standard probes: exploring new paths to constrain the expansion history of the Universe
Abstract:
The measurement of the local expansion rate of the Universe, the Hubble constant, has recently triggered an important scientific debate. It has been found that this quantity, when measured with local probes, shows a 4-sigma tension with the one extrapolated from the analysis of the high-redshift Universe with Cosmic Microwave Background. This issue, often referred to as the ‘Hubble tension’, is now one of the hot topics in physics. Exploring new and complementary approaches to measuring how the Universe (and the structures therein) have evolved has, therefore, become fundamentally important. This will increase the accuracy of the measurements and keep systematic effects under control. In this talk, I will discuss different approaches and methods that can be pursued to obtain independent constraints on the Universe’s expansion rate, recently reviewed in Moresco et al. (2022). I will present how cosmic chronometers, the ages of the oldest star in the Universe, and gravitational waves can be exploited as cosmological probes and how they can provide fundamental information in modern cosmology in the future.