Seminari


Il Dottorato in Astronomy, Astrophysics and Space Science incoraggia gli studenti a seguire in grande numero di seminari organizzati dagli istituti che organizzano il corso:
- Sapienza Università di Roma, dipartimento di Fisica
- Università degli studi di Roma "Tor Vergata", dipartimento di Fisica
- INAF, Istituto Nazionale di AstroFisica

Segue lista di seminari

2025


The Holographic Principle in de Sitter Space
08/07/2025
A great deal is known about quantum gravity in anti de Sitter space but almost nothing about the quantum theory of the more cosmologically relevant de Sitter space. I’ll explain recent developments in constructing holographic theories of de Sitter space and if there is time, the implications for cosmology.
Esplorare l'espansione dell'Universo con l'astronomia multi-messaggero
18/06/2025
Grazie alle sinergie tra gli esperimenti sulle onde gravitazionali (GW), come LIGO/Virgo/KAGRA e osservazioni elettromagnetiche di transienti e galassie, una varietà di nuove misurazioni cosmologiche è diventato possibile di recente. Molte di queste misurazioni si basano su l'uso degli eventi GW come "sirene standard". A seguito del rilevamento di la prima controparte elettromagnetica di un evento GW, GW170817, la è stata eseguita la prima misurazione della sirena standard "luminosa". Noi continuare a cercare controparti ottiche per consentire una maggiore luminosità analisi delle sirene con l'astronomia multimessaggera delle onde gravitazionali DECam Survey (GW-MMADS), per il quale descriverò i nostri recenti risultati. Misurazioni standard della sirena per eventi "oscuri", cioè senza un controparte elettromagnetica confermata, può anche essere eseguita, utilizzando correlazioni incrociate con i cataloghi di galassie o di nuclei galattici attivi. In in questa conferenza mostrerò le nostre ultime misurazioni standard delle sirene e previsioni e aspettative attuali per le rilevazioni multi-messaggero in nei prossimi anni.
Chasing the Light: Shadowing, Collimation, and the Rapid Growth of Infant Black Holes
18/06/2025
Observations with the James Webb Space Telescope (JWST) have uncovered a substantial population of high-redshift broad-line active galactic nuclei (AGNs) characterized by moderate luminosities, weak X-ray emissions, and faint high-ionization lines, challenging conventional models of AGN activity. In this talk, I will propose that these sources are accreting at super-Eddington rates and discuss how such accretion flows, shaped by thick disk geometries and anisotropic radiation fields, may provide new insights into black hole growth in the early Universe.
New measurements of H0 and dark matter properties based on JWST observations of lensed quasars.
17/06/2025
I will present new cosmological measurements based on JWST observations of strong gravitationally lensed quasars. In the first part of the talk, I will show the results of a multi-year effort by the TDCOSMO collaboration to use gravitational time delays to infer the expansion history of the universe and thus the Hubble constant. This method is completely independent of the local distance ladder and the cosmic microwave background, and thus provides a new opportunity to understand whether the tension between the two arises from systematic uncertainties or may be indicative of new physics. In the second part of the talk, I will use new JWST-MIRI observations of strongly lensed quasars and to detect dark subhalos independent of their stellar content. This measurement tests a fundamental prediction of the cold dark matter model, i.e. that galaxies should be surrounded by large numbers of dark satellite subhalos. I will discuss the implications of this measurement in terms of fundamental properties of dark matter, such as free streaming length and self-interaction cross section.
IAU Office of Astronomy for Education Center Italy: cosa è, cosa fa, perché lo fa in quel modo
11/06/2025
Fondato nel marzo 2021, l’Office of Astronomy for Education Center Italy (I-OAE) è un ufficio internazionale della IAU, coordinato e finanziato da INAF. In collaborazione con altri Centri, finanziamo corsi di formazione per insegnanti in decine di paesi nel mondo e organizziamo un congresso internazionale annuale. I-OAE sostiene pratiche di insegnamento innovativo e inclusivo, con apprendimenti centrato sulla persona e la creazione di una comunità di pratica nel bacino del Mediterraneo. Nei suoi primi anni di esistenza, I-OAE ha sviluppato una serie di processi collaborativi, a cui hanno partecipato rappresentanti di Albania, Cipro, Croazia, Egitto, Francia, Grecia, Israele, Italia, Marocco, Montenegro, Palestina, Portogallo, Slovenia, Siria, Spagna e Turchia. I-OAE coordina anche l’edizione internazionale di astroEDU, la piattaforma di attività didattiche peer-reviewed della IAU. I-OAE è un ufficio aperto alla collaborazione di volontari che ne condividano valori e metodi.
Seeking the New World of Spin Zero - Fundamental mysteries of nature and cosmic microwave background (CMB) polarization
06/06/2025
Particle cosmology is a discipline seeking a fundamental understanding of the Universe based on particle physics. Five mysteries drive our research today: cosmic inflation, baryon asymmetry, neutrino properties, dark matter, and dark energy. Resolving any of the five mysteries will revolutionize our picture of the Universe. Numerous interesting theoretical hypotheses have been proposed to this end. Many require new scalar particles, such as inflatons, axions, supersymmetric particles, etc. They are essentially an attempt to expand the role of the vacuum. Since we have not yet found such spin-zero particles, we shall invent new eyes to make an experimental or observational breakthrough. To this end, the observation of CMB polarization is one of the keys today. In this seminar, I focus on research topics to which I have contributed, including observations of CMB polarization for studying inflatons and searches for light axion-like particles.
Origin of Lunar Water and its Role in Enabling Sustainable Solar System Exploration
21/05/2025
The presence of water on the Moon and in lunar samples has emerged as one of the most exciting discoveries in recent times. Multiple sources are believed to have contributed to the lunar water inventory. Understanding the origin of lunar water holds significance that transcends scientific, technological, and societal domains. The Moon is becoming a favourite target for both established and emerging space-faring nations as well as commercial entities. In addition to national pride and scientific curiosity, the resurgence in lunar exploration is driven by a growing recognition of the Moon as a technology testbed for exploring more distant bodies within the Solar System. In this talk, I will outline our pioneering research which contributed to the discovery of water on the Moon and is shaping a vision for the future, envisioning a sustainable human presence on the lunar surface, largely facilitated by the in-situ use of resources, including water.
The latest results from the Dark Energy Spectroscopic Instrument (DESI): Is the Standard Cosmological Model in Question?
19/05/2025
The Dark Energy Spectroscopic Instrument (DESI) has constructed the largest 3-dimensional map of the universe to date, using millions of galaxies and quasars from its first three years of observations. The way this map evolves across space and time is determined by the relative contributions of ordinary matter, neutrinos, and the enigmatic dark matter and dark energy. Surprisingly, when DESI’s new data are combined with other probes, the standard cosmological model struggles to provide a coherent picture of the universe’s evolution. A simple extension of the model, where the dark energy equation of state varies over time instead of remaining constant, appears to better align with the observations. I will present these latest DESI results and explore their implications and future prospects.
Vera Rubin Observatory's Legacy Survey of Space and Time: The greatest movie of all time
13/05/2025
The Legacy Survey of Space and Time (LSST), the first project at the new Vera C. Rubin Observatory, will be the most comprehensive optical astronomical sky survey ever undertaken. Starting this year, Rubin Observatory will obtain panoramic images covering the sky visible from its location in Chile every clear night for ten years. The resulting 60 petabytes of raw imaging data, essentially a digital color movie of the night sky, will include about 20 billion galaxies and a similar number of stars, and will be used for investigations ranging from cataloging potentially hazardous near-Earth asteroids to fundamental physics such as characterization of dark matter and dark energy. I will briefly describe scientific goals behind this project that drove its design, illustrate the progress of its ongoing construction, and finish with a discussion of data analysis challenges that need to be tackled to make the best use of the massive and complex LSST dataset.
The X-ray Astrophysics of the Hot and Violent Universe
08/05/2025
X-rays reveal a hot and violent Universe. From the hot intracluster medium in clusters and groups of galaxies to gas swirling round black holes, X-rays provide vital information. High spatial resolution imaging and high spectral resolution spectroscopy reveal the role of black holes in the evolution of galaxies. I shall give a personal perspective on the development of our understanding over the past decades and include some recent results.
123

2024


Robust constraints on tensor perturbations from cosmological data: A comparative analysis from Bayesian and frequentist perspectives
20/12/2024
One of the central challenges in modern Cosmology is the precise characterization of the primordial tensor power spectrum, a cornerstone prediction of numerous cosmological models, particularly inflationary scenarios. These tensor perturbations carry distinctive imprints that can reveal their physical origins, making the robust reconstruction of their spectrum a pivotal goal for contemporary research. In this talk, I will present methods for constraining key parameters of the tensor power spectrum, such as the tensor-to-scalar ratio and the spectral tilt, with a particular emphasis on the statistical methodologies underpinning these inferences. I will critically examine the strengths and limitations of the standard Bayesian framework commonly employed in this context. Furthermore, I will demonstrate how complementary insights from a frequentist approach can deepen our understanding of the Bayesian results, offering a more nuanced perspective on the interplay between these statistical paradigms.
Wave dark matter
17/12/2024
We will explore the possibility that dark matter is composed of sufficiently light particles that it effectively behaves as a collection of waves. We will review the particle physics motivations and the rich wave phenomenology, and discuss the implications for astronomical observations and experimental detection.
Galaxy Clusters from adolescence to maturity: challenges for simulations
12/12/2024
In my talk I will review our understanding, through cosmological simulations, of the evolution of galaxy clusters from redshift z~2-3, to the recent cosmic epoch. Through a comparison with observational data at different wavelengths I will assess the capability of simulations to trace the fast evolution of such cosmic structures from their proto-cluster stage, characterized by a strongly star forming galaxy population embedded in a dynamically disturbed inter-galactic medium, to their relaxed stage at low redshift, characterized by a passive galaxy population immersed in a relatively relaxed intra-cluster medium. In this context, I will highlight successes of simulations, and critically assess their limitations and what we should learn from them.
Lighting up Blazar Physics at the Spectrum’s Edge: VHE and VLBI Synergies
12/12/2024
Blazars, a class of active galactic nuclei with jets aligned towards Earth, offer a unique opportunity to study extreme astrophysical processes. Their powerful jets emit across the entire electromagnetic spectrum, providing data at all wavelengths for investigation. This presentation focuses on the synergy between Very High Energy (VHE) gamma-ray observatories and VLBI arrays—two distinct facilities operating at opposite ends of the spectrum—used to uncover the mechanisms driving the non-thermal emission of blazars. VHE observations probe the highest energy emissions from these objects, while VLBI provides high-resolution imaging of their jet structures. Together, they enable the study of particle acceleration processes, jet kinematics, and emission variability across multiple scales. I will introduce the basics of VHE observations and the tools employed at the two extremes of the spectrum. Finally, I will present studies showing how this combined approach deepens our understanding of blazar physics, from the origins of high-energy photons to the dynamic behaviour of jets in their most compact regions.
Breaking the distance-duality relation to address cosmic tensions
11/12/2024
Persistent cosmic tensions arise from discrepancies in the cosmological distance ladder constructed from different distance observables, such as BAO and SnIa, which are calibrated using measurements from either the early or late Universe. These tensions are typically evaluated under the assumption that the distance-duality relation (DDR) holds, allowing for a direct comparison between measurements of the luminosity and angular diameter distances. In this talk, we will examine the implications of relaxing this assumption and considering more general relations. We will discuss how this approach impacts the interpretation of current cosmic tensions and its potential to clarify whether new physics is needed to address these discrepancies.
Extended AGN jets as a direct test to the ΛCDM model
03/12/2024
Current small-scale cosmological controversies are coming down to the precision level of observations. The key point is whether a better understanding of baryonic physics, dark matter physics, or both is required to address these challenges. In this talk, I will describe how very long baseline interferometric observations of extended AGN jets (sometimes gravitationally lensed) are contributing to understanding some of these small-scale cosmological issues while simultaneously providing insights on the jet physics up to the earliest epochs (z>6).
The nature and fate of the most obscured high-z massive galaxies
28/11/2024
The early assembly of the most massive galaxies, and their contribution to the SFR density of the universe is currently one of the main challenges for galaxy formation models. Recently, a population of massive red sources already in place at z>2-3 have been discovered, and called HST-dark, because they are missed by optical/UV search but detected at MIR and often in the mm. Their characterisation remains uncertain, due to limited information available, and to different selection techniques. JWST is now allowing us to investigate the nature of HST-dark galaxies, and to reveal new populations of early massive galaxies. I will discuss the main properties of HST-dark galaxies, compared to those of JWST NIR-dark. For those ALMA detected, the molecular gas mass and depletion times show that they are likely on the way to quenching their SF. For ALMA HST-dark, there is a consensus on the presence of large amounts of dust, posing the problem of high-z dust production. To constrain dust properties and obscured SF at high-z we need to observe in the FIR. I will present the recently selected NASA PRobe far-Infrared Mission for Astrophysics (PRIMA), a FIR (25-235 μm) observatory operating in the 2030s in spectroscopy and imaging, that will allow us a leap forward in our knowledge of the high-z obscured universe.
Gamma-Ray Burst Polarimetry: History and Future Prospects
25/11/2024
Gamma-Ray Bursts (GRB) are the brightest electromagnetic events in the Universe since the Big Bang. As such they have intrigued the astrophysical community since their accidental discovery in 1967. Despite almost 60 years of intense research, resulting in over 10000 GRB detections, very little remains known about these violent events. While we know that these events are related to the death of massive stars or the merger of compact objects, we still lack an understanding of how, and where, the gamma-rays which give these events their name, are produced. Attempts to understand this have thus far focussed primarily on measurements of the time of arrival, the direction and energy of the gamma-ray emission. Measurements of the 4th parameter, the polarization, are rare, despite their significant potential to resolve theoretical models. In this talk I will discuss this potential in detail, while in parallel addressing the reasons for the lack of polarization measurements. Finally, I will present an overview of past missions as well as the missions which aim to provide the first detailed measurements in the coming decade.
Recent observations of the near-Earth radiation environment: a plethora of galactic, solar and magnetospheric particles
22/11/2024
The near-Earth radiation space is a unique environment where particle populations of different origins coexist and evolve dynamically over time and space, spanning a wide energy range. Galactic cosmic rays – entering the heliosphere – are continuously modulated by the change in the solar wind and the associated heliospheric magnetic field. Moreover, changes in galactic particle fluxes show a very clear time-dependence, which is directly related to the periodical activity of the Sun. However, the Sun acts as both a modulator and a source of space radiation – especially during maxima of solar activity – with powerful emissions of the so-called solar energetic particles (SEPs). Despite notable improvements in the latest decades, the complex mechanisms underlying their origin and transport still challenge the development of a comprehensive picture of SEP events. Many efforts have also been directed at modelling the Earth’s trapped charged particle environment, as in the case of the South Atlantic Anomaly (SAA). Observations of the SAA radiation environment are crucial to validate these models (e.g., the NASA AE9/AP9 models), as well as to investigate the temporal evolution of the geomagnetic field, to study perturbations generated by space weather events (such as geomagnetic storms), and, last but not least, to safeguard spacecraft systems and human crew health. After the foundational results of successful past (PAMELA) and present (AMS-02) spaceborne missions, the CSES (China Seismo-Electromagnetic Satellite) mission aims to continue the study of the near-Earth radiation environment, through a constellation of low-Earth orbit satellites. This presentation will review the main results achieved by the High-Energy Particle Detector (HEPD-01) on board the CSES-01 satellite, which will be followed by the launch of the improved HEPD-02 detector on the CSES-02 satellite in December 2024.
Magnetic field amplification in neutron star mergers and the role of the MRI
21/11/2024
The first detection of a binary neutron star merger has made sharp reality the long-standing paradigm that these cosmic fireworks are exciting laboratories for extreme physics. To get the most out of present and future observations, however, we require accurate models of the merger dynamics, which can only be achieved through numerical relativity simulations. One of the key factors in these simulations is the magnetic field, which plays a crucial role in shaping the dynamics of the system. It is also instrumental in the launching of relativistic jets and the associated gamma-ray bursts. In this seminar I will discuss the main mechanisms responsible for the amplification of the magnetic field, with a particular focus on the magneto-rotational instability and its potential role in binary neutron star mergers."
1234567

2023


Towards the geology of exoplanets
20 Aprile, 2023, ore 16:30 CEST
Hot rocky exoplanets offer exciting opportunities to place terrestrial geology into Galactic context, through composition measurements with JWST and Ariel. To capitalise on these opportunities we must identify the very best targets for spectroscopic characterisation. The catastrophically disintegrating exoplanets (CDEs) are the most dramatic examples of mass loss from an ablating rocky surface. They were discovered by Kepler through the variable transits of dust co-existing with metal-rich vapour, and are particularly suitable for transmission spectroscopy because the ablated material is spread over a large scale-height. But the Kepler CDEs are too faint for transmission spectroscopy. The Dispersed Matter Planet Project (DMPP) is discovering the nearby analogues and progenitors of the Kepler CDEs. DMPP uses archival stellar spectra to identify stars we view through shrouds of diffuse, metal-rich, circumstellar gas. The underlying hypothesis is that the gas is ablated from hot, close-orbiting planets. DMPP searches for the putative planets with high-precision, high cadence radial velocity measurements. The approach has been extremely successful and efficient, with planet discoveries whenever 60 RV measurements have been collected. DMPP-1 is a compact multiplanet system orbiting a star brighter than V=8. A possible CDE transit has been discovered in TESS data. DMPP-2 b is the joint-first RV planet discovery orbiting a strongly pulsating star. DMPP-3 is an eccentric binary star system with the secondary at the mass threshold for sustaining hydrogen fusion. A 2.6 Earth mass planet orbits the K0V primary star in a 6.7 day orbit, with a second Earth-mass circumprimary planet marginally detected. DMPP-3AB is in a hitherto unpopulated parameter space for binary star planetary systems. I will include updates on our latest discoveries of around 20 short period planets, including planets orbiting a star of magnitude 6, and planets orbiting a young star. We may have caught the latter system in the act of evolving out of the Neptune desert through planetary ablation. DMPP planets are likely to be viewed edge-on as ablated material will remain concentrated near the planets’ orbital planes. Thus they have high transit probability. The subset of DMPP planets which transit are thus amenable to direct empirical determinations of mass, radius and composition.

2022


Annalisa Pillepich, Max Planck Institute for Astronomy, Heidelberg: The many diverse manifestations of supermassive black-hole feedback: from simulations to observations, and back
26 ottobre 2022
Large-volume cosmological galaxy simulations, such as IllustrisTNG, provide a holistic view on galaxies and on how their evolution depends on the interplay of internal and external physical phenomena. Among the internal mechanisms, feedback from super massive black holes (SMBHs) is commonly invoked in such numerical models to halt star formation in massive galaxies. In fact, no other mechanism so far has been shown to be capable of returning entire populations of simulated massive quenched galaxies that are consistent with the observed galaxy red sequence and quenched fractions. With simulations like IllustrisTNG we are putting together ever more quantitative and plausible evidences as to the role that feedback from SMBH can have, not only in shaping galaxy structural properties and galaxy populations across 90 per cent of the Universe’s history, but also in regulating the thermodynamical, ionization, and metal enrichment properties of the cosmic gas across halo scales and beyond. In this talk, I will use the outcome of the IllustrisTNG and other simulations in combination with current and future observational data, chiefly SDSS galaxy data and eROSITA X-ray observations, to further our understanding of the tight interconnections between SMBHs, star-formation quenching, and the physical state of the circumgalactic medium.
Pascal Oesch, University of Geneva: Galaxy Build-up During the Cosmic Reionization Epoch
4 luglio 2022
Speaker: Pascal Oesch (University of Geneva) Title: Our Panchromatic View of Galaxy Build-up at Cosmic Dawn into the JWST Era Abstract: The first deep images with the Hubble Space Telescope (HST) have transformed our view of the Universe. Over the following more than two decades, HST continued to extend our cosmic horizon reaching to only ~400 Myr after the Big Bang at z~11. In combination with other observations across the electromagnetic spectrum, from the rest-frame optical with Spitzer/IRAC, and now all the way to (sub)mm wavelengths with ALMA/NOEMA, we are gaining a more and more complete census and understanding of galaxy build-up across 97% of cosmic history. Yet some critical gaps remain, mainly because (1) our galaxy samples are still mostly rest-UV selected at z>3, and (2) we still only have highly-incomplete spectroscopic information at z>6. In this talk, I will present an overview of our current understanding of star-forming galaxies at z>3 based on our panchromatic view from HST+Spitzer+ALMA/NOEMA data. This will be completely revolutionized over the next months, however, as the first observations with the JWST are being taken. In particular, JWST will provide deep rest-frame optical data out to z=10, both in imaging and spectroscopy, which is truly unprecedented. JWST will thus finally allow us to probe the physics of the first generations of galaxies that ended the cosmic Dark Ages and started the reionization of the Universe. Join Zoom Meeting https://uniroma1.zoom.us/j/81122901013?pwd=M1hnRHRXZkEyeW1QMFlPQ2FXa0dNZz09 ID riunione: 811 2290 1013 Passcode: 686688
Elena Maria Rossi, Leiden Observatory: A multi-tracer study of the Local Group of galaxies
8 giugno 2022
The Local Group, and the Milky Way in particular is a unique laboratory to study the process of galaxy assembly because of our vantage point. This is especially true in this era of current and up-coming (all sky) surveys like e.g. Gaia, WEAVE, 4MOST, DASI, LSST, and Euclid, that are delivering an unprecedented astrometric, spectroscopic and photometric view of the Galactic stellar population. In this talk, I will review my group's work --both theoretical and observational -- towards the understanding of the mass distribution and other properties of the Milky Way using different dynamical tracers such as stellar streams and hypervelocity stars. Looking at the future, I will also show my vision for Galactic studies in the LISA era, when gravitational waves will deliver complementary information with respect to electromagnetic waves.
Samaya Nissanke, University of Amsterdam: Gravitational waves and multi-messenger astrophysics
26 maggio 2022
Abstract: Since the revolutionary discovery of gravitational wave (GW) emission from a binary black hole merger in 2015, the exquisite GW detectors LIGO, Virgo and KAGRA have detected more than 90 compact object mergers. Most notably, one of these mergers corresponds to the first binary neutron star merger, dubbed GW170817. This event has been transformative because it was observed in both gravitational and electromagnetic radiation, thus opening up a new era in multimessenger astrophysics. The multi-messenger characterisation of such an event has enabled major advances into diverse fields of modern physics from gravity, high-energy and extragalactic astrophysics, nuclear physics, to cosmology. In this talk, I will discuss work in strong-field gravity astrophysics and how combining observations, theory and experiment is key to make progress in this field. I will present the opportunities and challenges that have emerged in multi-messenger astrophysics, and what the future holds in this new era. Join Zoom Meeting https://uniroma1.zoom.us/j/81122901013?pwd=M1hnRHRXZkEyeW1QMFlPQ2FXa0dNZz09 ID riunione: 811 2290 1013 Passcode: 686688
Rachel Somerville, Center for Computational Astrophysics Flatiron Institute: Developing new galaxy formation models that will help us Learn the Universe
5 maggio 2022
Understanding and simulating galaxy formation from first principles is a huge computational challenge because of the vast range of scales and rich array of physics involved. Upcoming experiments will map galaxies and gas across unprecedented volumes and probe further back into cosmic time than ever before. These experiments have the potential to probe fundamental physics questions such as the nature of dark matter and dark energy, and the initial conditions of the Universe. But in order to extract the full scientific potential from these data, we need to understand how luminous tracers (stars and gas) are related to the underlying matter density field, and we must develop techniques that can accurately forward model the galaxy formation process with a computational efficiency that is orders of magnitude higher than standard numerical hydro/N-body techniques. I will describe the philosophy and status of the SMAUG (Simulating Multiscale Astrophysics to Understand Galaxies) project, and how it will form a pillar in the new Simons Collaboration "Learning the Universe", which will combine new galaxy formation models, new machine learning techniques, and simulation based inference to obtain constraints on cosmology and astrophysics.
Georges Meynet, University of Geneva: Stars at the Extreme: First Stars, Spinstars and Supermassive Stars
6 aprile 2022
The presentation will focus on stars at some extreme either from the point of view of their mass (supermassive stars), rotation (spinstars) or initial composition (Pop III stars). The talk will begin by a general overview of the main challenges faced by the modeling of massive stars with a special focus on the transport processes in convective and radiative zones. Then the presentation will continue discussing recent results about the binary statistics of Pop III populations, the chemical and radiative feedback of Pop III stars, the evolution of very massive stars i.e. stars with masses between 150 and 300 solar masses at different metallicities addressing the question of the progenitor of Pair Instability supernovae and the limits of the mass domain for the black hole mass gap. Finally, new models for the formation of supermassive stars that are candidates as seeds for the formation of supermassive black holes at high redshift will be presented
Felix Aharonian, Dublin Institute for Advanced Studies and Max-Planck-Institute for Nuclear Physics (MPIK), Heidelberg, Germany: PeVatrons and the "Century-old-Mistery" of Galactic Cosmic Rays
2 marzo 2022
Despite the recent advances in Cosmic Ray studies, the origin of Galactic Cosmic Rays (CRs) is still considered a "century-old mystery" - we do not know yet which sources contribute to CR fluxes measured in the Earth's vicinity. Identifying the major CR contributors with astronomical source populations is one of the highest priorities of the field. The best carriers of information about CR factories are gamma-rays and neutrinos - the only stable and neutral secondary products of CR interactions pointing to the CR production sites. The recent years' outstanding achievement of gamma-ray astronomy was the discovery of TeV gamma-radiation from SNRs generally supporting the SNR paradigm of the origin of Galactic CRs. On the other hand, the lack of the extension of gamma-ray spectra of young SNRs well beyond 10 TeV raises doubts about their ability to contribute to the highest energy galactic CR spectrum in the so-called "knee" region above 1 PeV. Meanwhile, the ultra-high-energy (UHE; E> 100 TeV) gamma-ray observations of the clusters of young massive stars demonstrate mounting evidence of these objects (and related superbubbles) being prime contributors to Galactic CRs at PeV energies. I will discuss these observations in the context of the concept of "Young Stars versus Dead Stars". The hunt for CR PeVatrons cannot be reduced merely to the identification of the sources contributing to the local "CR fog". The term 'cosmic rays' has broader implications; after matter, radiation and magnetic fields, the relativistic nonthermal plasma constitutes the fourth substance of the observable Universe. The localisation and exploration of physical conditions and processes in these extreme CR factories, independent of their relative contributions to the 'CR fog', is a fundamental issue in its own right. I will highlight the recent exciting achievements of UHE gamma-ray astronomy in elucidating the cites of extreme CR accelerators in the Milky Way and discuss the implications of the discovery of a large number of CR PeVatrons by the LHAASO collaboration.
Volker Bromm, University of Texas at Austin: What do we know about the first stars and galaxies?
8 febbraio 2022
I will review the emerging theoretical framework for how stars, galaxies, and black holes transformed the early universe. Predictions for the enrichment of the intergalactic medium with heavy chemical elements, the rate of supernova explosions and gamma-ray bursts, as well as the number density and properties of the first galaxies, sensitively depend on the particle-physics nature of dark matter. To constrain the elusive first generation of stars, we can bring to bear a powerful combination of probes at high redshifts and in our local neighborhood. The latter approach, known as “stellar archaeology” holds particular promise in light of ongoing and planned large surveys of metal-poor stars, both in the Milky Way and its dwarf satellites. It is exciting to contemplate the decade ahead, when the James Webb Space Telescope (JWST) will allow us to confront theory with observations at the edge of time.

2021


Licia Verde, ICREA and Institute of Cosmological Sciences, University of Barcelona: "The future beyond precision cosmology"
14/12/2021
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.
Samaya Nissanke, University of Amsterdam: "Gravitational waves and multi-messenger astrophysics"
30/11/2021

Giovanna Tinetti, Department of Physics and Astronomy, University College London: "Decoding the light from other worlds"
09/11/2021
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.
Pavel Kroupa, University of Bonn and Charles University of Prague: How observations of stellar populations constrain cosmological models
19/10/2021
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.
Ralf Klessen, Institute for Theoretical Astrophysics, University of Heidelberg: Star formation through space and time
23/09/2021
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.
Piero Madau, Department of Astronomy and Astrophysics, University of California Santa Cruz: The dark and luminous side of structure formation
22/06/2021
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.
Debora Sijacki, Institute of Astronomy, University of Cambridge, UK: The evolution of massive black holes through cosmic times
01/06/2021
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.
Roberto Maiolino, Cavendish Laboratory, University of Cambridge, UK: Quenching star formation in galaxies
18/05/2021
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.
Joseph Silk, Institut d’Astrophysique de Paris, The Johns Hopkins University, University of Oxford: The future of cosmology
16/04/2021
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.
Benedetta Ciardi, Max Planck Institute for Astrophysics: Exploring cosmic reionization with 21cm telescopes
09/03/2021
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 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. Join Zoom Meeting https://uniroma1.zoom.us/j/89931306878?pwd=WG5RYlYyZzRSMzJsOFpSRHczWEFCZz09
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