ASTRONOMY ASTROPHYSICS AND SPACE SCIENCE

Seminars

The PhD program in Astronomy Astrophysics and Space Science encourages students to follow the wide range of seminars organised by the institutes hosting the course:
- Sapienza University of Rome, Physics Department
- Tor Vergata University of Rome, Physics Department
- INAF, National Institute of Astrophysics

See below for a list of seminars

2023

Towards the geology of exoplanets
April 20, 2023, 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
Oct 26th, 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
July 4th, 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
June 8t, 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
May 26th, 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
May 5th, 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
April 6th, 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
March 2, 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?
Feb 8, 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

Razmik Mirzoyan, Max Planck Institute for Physics, Munich, Germany: Gamma-Ray Astronomy: The Cross-Road Between Physics and Astrophysics
23/02/2021
hirty-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. Join Zoom Meeting https://uniroma1.zoom.us/j/89931306878?pwd=WG5RYlYyZzRSMzJsOFpSRHczWEFCZz09

Cecilia Ceccarelli, Université Grenoble Alpes, IPAG: The astrochemical trail of our origin
02/02/2021
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.