Slava Mukhanov (LMU, Munich)
Resolving Singularities in General Relativity
Friday, June 7th, 2024, 11:30am – Room 128-129 at SISSA (via Bonomea 265) & streaming

Abstract. I will discuss how a rather minimal modification of the Einstein equations at high curvatures can easily resolve the singularities in a collapsing Friedmann Universe, in an anisotropic Kasner Universe and inside black holes.

Contact: Stefano Liberati

Jia Liu (IPMU, Tokyo)
Cosmology with massive neutrinos
Friday, May 31st, 2024, 11:30am – Aula D (old SISSA building) & streaming

Abstract. Ghostly neutrino particles continue to bring surprises to fundamental physics, from their existence to the phenomenon of neutrino oscillation, which implies their nonzero masses. Their exact masses, among the most curious unknowns beyond the Standard Model of particle physics, can soon be probed by the joint analysis of ongoing and upcoming cosmological surveys including Rubin LSST, Euclid, Roman, DESI, PFS, Simons Observatory, CMB-S4, and LiteBRID. In this talk, I will discuss ongoing works studying the effects of massive neutrinos and will draw a roadmap towards discovering the neutrino mass over the next decade.

Contact: Carlo Baccigalupi
VideoJia Liu’s webpage

Pasquale Panuzzo (Observatoire de Paris)
Gaia BH3: a 33 solar mass dormant BH discovered in Gaia preliminary data
Friday, May 24th, 2024, 11:30am – Aula D (old SISSA building) & streaming

Abstract. The validation activities in preparation of the Gaia DR4 resultes in the discovery (Gaia collaboration, Panuzzo et al, 2024) of a binary system hosting a dormant black hole with an exceptional mass: 33 times our Sun. Its mass makes it the most massive black hole of stellar origin discovered in our Galaxy so far. The system, named Gaia BH3, was found from the preliminary astrometry, and confirmed by Gaia RVS and ground based radial velocity measurements. Broad-band photometric and spectroscopic data show that the visible component is an old, very metal-poor giant of the Galactic halo. The BH in the Gaia BH3 system constitutes the only example in our Galaxy of the high mass black holes that have been detected in BH mergers, in distant galaxies via gravitational waves, by LIGO/Virgo/KAGRA consortium. The fact that the stellar companion is a very metal-poor giant strongly supports the scenario that the progenitors of the high-mass BHs detected by gravitational-wave telescopes are metal-poor massive stars (Belczynski et al. 2016). It is also worth noting that the mass of Gaia BH3 is close to the peak of the observed mass distribution for the merging BHs (e.g. Farah et al. 2024). The Galactic orbit of the system and its metallicity indicate that it belongs to the ED-2 stream (Balbinot et al 2024), likely a globular cluster accreted by the Milky Way, giving hints on the formation mechanism of this binary system. In fact, it is predicted (Rastello et al. 2023; Tanikawa et al. 2024; Di Carlo et al. 2024; Pina et al. 2024) that dynamical formation of detached star-BH binaries is more efficient than isolated binary formation. In the case of Gaia BH3, the latter mechanism cannot be excluded (El-Badry 2024). Gaia BH3 is the third dormant black hole discovered from Gaia data (El-Badry et al. 2023a,b; Tanikawa et al. 2023; Chakrabarti et al. 2023), and it is expected to be followed by a number of BH-hosting binaries in the next release, which will help to formulate a comprehensive view of BH formation and the evolution of their progenitors. In this talk, we will describe the discovery of Gaia BH3, its implications, and report on first results obtained by the community on this astonishing object.

Contact: Alessandro Bressan
VideoslidesPasquale Panuzzo’s webpage

Eric Linder (Lawrence Berkeley National Laboratory)
Who’s Afraid of Dark Energy?
Friday, May 17th, 2024, 11:30am – Aula D (old SISSA building) & streaming

Abstract. Cosmic acceleration dominates the behavior of the recent universe, with some fundamental new physics at its heart. Recent data gives a tantalizing suggestion that the dark energy behind it is more complicated than a cosmological constant. Nevertheless, I emphasize that there is quite a lot that we do know about how to describe dark energy behavior, and great promise for further insight from data within the next year.

Contact: Matteo Viel
VideoEric Linder’s webpage

Pasquale Blasi (Gran Sasso Science Institute)
On a self-regulated escape of cosmic rays from sources
Friday, May 10th, 2024, 11:30am – Aula D (old SISSA building) & streaming

Abstract. The escape of accelerated particles from their sources, to become cosmic rays, is a complex and poorly understood phenomenon. Recent theoretical advances and new observations of high energy radiation from the regions around sources are shedding some light on this phenomenon, so crucial to shape the spectrum of particles that we receive at the Earth or that we infer from indirect observations. I will discuss these aspects with emphasis on self-confinement, namely the generation of electromagnetic  perturbations induced by cosmic ray currents, with applications to supernova remnants, pulsar wind nebulae and sources of ultra high energy cosmic rays.

Contact: Piero Ullio
VideoPasquale Blasi’s webpage

Tirthankar Choudhury (NCRA, Pune)
Cosmic Neutral Hydrogen: A Probe of the First Stars in our Universe
Friday, April 5th, 2024, 11:30am – Aula D (old SISSA building) & streaming

Abstract. Detecting the signatures of the very first stars in our Universe offers a promising avenue for understanding cosmic evolution. These stars leave their imprint on the large-scale distribution of cosmological hydrogen through the process of reionization, driven by the photoionization of hydrogen atoms by ultraviolet photons. The evolution of reionization serves as a valuable tool not only for investigating the properties of galaxies in the early Universe, but also for constraining cosmological models. In this presentation, we provide an overview of ongoing and upcoming observational probes for studying reionization, alongside recent advancements in theoretical modelling. Furthermore, we outline future prospects for detecting the signatures of the first stars utilizing cutting-edge telescopes such as the SKA, highlighting interesting findings from our research group.

Contact: Matteo Viel
VideoTirthankar Choudhury’s webpage

José Manuel Carmona (University of Zaragoza)
QGMM network: theoretical and experimental challenges and opportunities for research in quantum gravity phenomenology
Friday, January 19th, 2024, 11:30am – Aula D (old SISSA building) & streaming

Abstract. The experimental search of non-conventional effects predicted by bottom-up approaches and theoretical models of quantum gravity is a quite recent field of research. Generically, it requires to consider probes of very high-energy and amplification mechanisms, conditions which are fulfilled by the propagation of the cosmic messengers. Advances in multi-messenger astronomy during the last decade has driven progress in the field, but a number of theoretical and experimental challenges still lie ahead. In order to tackle them, collaboration between theorists experts in the phenomenology of quantum gravity models and the various experimental communities involved in the detection of the cosmic messengers (high-energy gamma rays and neutrinos, ultra high-energy cosmic rays, and gravitational waves) is essential. Such collaboration has effectively started with the establishment of the QGMM network, born from the community joined together within the recently finished COST Action CA18108 “Quantum gravity phenomenology in the multi-messenger approach”. In this colloquium we will describe some of the challenges identified within this network and an outlook of the opportunities that future exploration may offer for the advancement of the field of quantum gravity phenomenology.

Contact: Stefano Liberati
VideoSlidesJosé Carmona’s Webpage

Avery Meiksin (University of Edinburgh)
Revealing the Dark Ages in 21-cm radiation
Friday, December 1st, 2023, 11:30am – Aula D (old SISSA building) & streaming

Abstract. After primordial hydrogen and helium from the Big Bang recombined when the Universe was a few hundred thousand years old, the Universe remained dark for another half billion years until Cosmic Dawn, when the first radiation sources appeared. While the individual sources were too dim to detect directly, they may be revealed indirectly through a 21-cm signal produced by their impact on neutral intergalactic hydrogen, including driving the last major phase change in cosmological baryons from neutral to ionized during the Epoch of Reionization. The discovery of the 21-cm signal is now a primary science goal for a new generation of radio telescopes. I will discuss the physical origin of the signal, what it may tell us about the first radiation sources and the progress made to date toward its detection.

Contact: Matteo Viel

Anna Bonaldi (Manchester University)
The Square Kilometre Array Observatory: current status and science preparatory activities
Friday, November 10th, 2023, 2:00pm – Aula D (old SISSA building) & streaming

Abstract. The Square Kilometre Array (SKA,, currently under construction, will be the world’s largest radio observatory once completed. It will consist of one radio telescope operating in the 50-350 MHz frequency range (SKA-Low, Western Australia) and another one operating in the 350 MHz-15 GHz range (SKA-Mid, South Africa). I will describe the SKA’s science drivers and give an update on the current construction activities, with a focus on the Italian contributions. I will describe the Observatory’s timeline and access policy. I will finally describe the current science preparatory activities, in particular the SKA science data challenges.

Contact: Tommaso Ronconi

Francesca Matteucci (Università di Trieste)
Galactic archaeology: a natural history of the Milky Way
Friday, October 13th, 2023, 11:30pm – Aula D (old SISSA building) & streaming

Abstract. Galactic archaeology allows us to reconstruct the history of  star formation and evolution of galaxies by means of chemical abundances. Most of the attention is paid to  the Milky Way for which we have now the largest amount of observational data. In the last years, in fact, large stellar spectroscopic surveys of the Milky Way have allowed us to compare theoretical chemical evolution models to data and infer important constraints on the history of our Galaxy. I will first explain how to build detailed chemical models and discuss the main necessary  ingredients I will then review and interpret the highlights in the chemical evolution of the Milky Way,  such as the observed bi-modality in the [alpha/Fe] ratios in the stars of the thick and think disc, the different stellar populations inhabiting the bulge, the abundance gradients along the thin disc and their evolution with time. I will also discuss the formation of neutron capture elements, such as Europium, by merging neutron stars and supernovae core-collapse. The possibility that the stellar Galactic halo was formed by stars accreted from dwarf satellites will be also discussed by means of specific chemical clocks. The Lithium cosmological problem, which involves Galactic halo stars, will be finally presented.