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9 Oct 2024 - Dr. Luca Comisso (Columbia University, USA)
"Unraveling Particle Acceleration and Pitch-Angle Anisotropy: Insights from Magnetized Turbulence and Magnetic Reconnection"
9 Oct 2024 - Dr. Luca Comisso (Columbia University, USA)
"Unraveling Particle Acceleration and Pitch-Angle Anisotropy: Insights from Magnetized Turbulence and Magnetic Reconnection"
Abstract: Radiation emitted by nonthermal particles accelerated in highly magnetized environments is crucial for understanding the nonthermal emission in a variety of astrophysical systems. When attempting to decipher the radiative emission from the energized particles, accounting for their energy distribution alone may not be sufficient to determine the emission’s properties. In environments with strong magnetic fields—where processes like magnetized turbulence and/or magnetic reconnection play a key role—understanding the pitch-angle distribution becomes necessary. In this talk, I will discuss how particle acceleration in highly magnetized plasmas gives rise to anisotropic particle distributions, characterized by broken power laws in the particle energy spectrum and pitch-angle anisotropy. I will discuss the implications of these anisotropic pitch-angle distributions in a variety of astrophysical plasmas. If time permits, I will also discuss how some of these insights relate to the acceleration of ultrahigh-energy cosmic rays, the most energetic particles to reach Earth, in light of the Pierre Auger Observatory’s spectrum and composition measurements.
Speaker information: https://lucacomisso.com/
23 Oct 2024 - Dr. Georgios Pantolmos (NKUA, Greece) **in person**
"The inner environments of newborn Sun-like stars through global numerical simulations"
23 Oct 2024 - Dr. Georgios Pantolmos (NKUA, Greece) **in person**
"The inner environments of newborn Sun-like stars through global numerical simulations"
Title: The inner environments of newborn Sun-like stars through global numerical simulations
Abstract: Classical T Tauri stars (CTTs) are young (~ Myr old), low-mass, and magnetized stellar objects, which accrete matter from their surrounding accretion disks. CTTs are classified as variable objects (e.g., with irregular light curves) and their variability, outcome of the complex dynamical interactions between the star and its circumstellar disk, is still not well understood. Furthermore, observations show that CTTs are slow rotators and in spin equilibrium during their lifetimes despite steadily accreting both mass and angular momentum. A conclusive answer on the physical processes governing the magnetic braking of the central object does not exist. In this seminar I will present the outcome of global MHD simulations of star-disk interactions, which attempt to produce the large-scale dynamics of the CTTs inner environments (< 0.1 AU), further focusing on the mechanisms that can possibly explain the CTTs observed variability and slow rotation.
Title: The inner environments of newborn Sun-like stars through global numerical simulations
Abstract: Classical T Tauri stars (CTTs) are young (~ Myr old), low-mass, and magnetized stellar objects, which accrete matter from their surrounding accretion disks. CTTs are classified as variable objects (e.g., with irregular light curves) and their variability, outcome of the complex dynamical interactions between the star and its circumstellar disk, is still not well understood. Furthermore, observations show that CTTs are slow rotators and in spin equilibrium during their lifetimes despite steadily accreting both mass and angular momentum. A conclusive answer on the physical processes governing the magnetic braking of the central object does not exist. In this seminar I will present the outcome of global MHD simulations of star-disk interactions, which attempt to produce the large-scale dynamics of the CTTs inner environments (< 0.1 AU), further focusing on the mechanisms that can possibly explain the CTTs observed variability and slow rotation.
6 Nov 2024 - Prof. Lara Nava (INAF, Brera Astronomical Observatory, Italy)
6 Nov 2024 - Prof. Lara Nava (INAF, Brera Astronomical Observatory, Italy)
"Very-high energy emission form Gamma-ray bursts"
Title: Very high energy emission from Gamma-ray bursts: new methods to unveil the mystery of these cosmological sources
Abstract: Gamma-ray bursts (GRB) are cosmological, transient sources producing radiation on a very wide range of frequencies, from the radio band to soft gamma-rays. The origin of the emitted radiation is ascribed to the presence of an ultra-relativistic jet (with typical Lorentz factor of ~100-300) undergoing energy dissipation within the outflow itself and in interactions between the outflow and the surrounding medium (internal and external dissipation, respectively). In this talk, I review the status of our understanding of the physical processes responsible for the radiation. In particular, I will focus on the recent detections of very-high energy emission (around TeV energies) and on its possible use to improve our understanding of GRBs and of particle acceleration in these extreme environments. Detections of multi-TeV emission from cosmological GRBs are expected to have a huge impact on models of the extragalactic background light (EBL), Lorentz invariance violation, and axion-like particles, especially once the advent of the Cherenkov Telescope Array (CTA) will allow us to study VHE radiation from GRBs in a more systematic way.
20 Nov 2024 - Prof. Lidia Oskinova (Potsdam University, Germany)
20 Nov 2024 - Prof. Lidia Oskinova (Potsdam University, Germany)
"Massive stars in the era of gravitational wave astrophysics"
Title: Massive Stars in Low-Metallicity Galaxies: Right Here and Far, Far Away
Abstract: Massive stars - those with much greater mass than our Sun - are hot, luminous, and live brief but influential lives, ending in gravitational collapse to form neutron stars or black holes. As cosmic powerhouses, these stars shape conditions in star-forming galaxies across cosmic time and played a crucial role in re-ionizing the early Universe. Recent advancements, including gravitational wave observations and discoveries of young galaxies by the JWST, have brought massive star research into the astrophysical spotlight.
Title: Massive Stars in Low-Metallicity Galaxies: Right Here and Far, Far Away
Abstract: Massive stars - those with much greater mass than our Sun - are hot, luminous, and live brief but influential lives, ending in gravitational collapse to form neutron stars or black holes. As cosmic powerhouses, these stars shape conditions in star-forming galaxies across cosmic time and played a crucial role in re-ionizing the early Universe. Recent advancements, including gravitational wave observations and discoveries of young galaxies by the JWST, have brought massive star research into the astrophysical spotlight.
However, these findings have also exposed major gaps in our understanding of how massive stars and binaries evolve and die, especially in low-metallicity environments. In this talk, I will review the current state of our knowledge on massive stars and high-mass X-ray binaries in low-metallicity galaxies, outline pressing gaps in our understanding, and explore the critical impact of massive stars and their feedback across cosmic time.
However, these findings have also exposed major gaps in our understanding of how massive stars and binaries evolve and die, especially in low-metallicity environments. In this talk, I will review the current state of our knowledge on massive stars and high-mass X-ray binaries in low-metallicity galaxies, outline pressing gaps in our understanding, and explore the critical impact of massive stars and their feedback across cosmic time.
Speaker information: https://lidiaoskinova.wordpress.com/wordpress
27 Nov 2024 - Dr. Athanasios Papaioannou (IAASARS, NOA, Greece) ** in person **
"Preparing for Space Odyssey: Predicting Solar Storms"
27 Nov 2024 - Dr. Athanasios Papaioannou (IAASARS, NOA, Greece) ** in person **
"Preparing for Space Odyssey: Predicting Solar Storms"
Title: Preparing for Space Odyssey: Predicting Solar Storms
Abstract: Solar Energetic Particle (SEP) event predictions are of particular importance for the near-future planned manned missions to the Moon and Mars, as well as for our unimpeded daily living. In this review, key findings that have been utilized and/or explored by the scientific community over the last decades to establish prediction schemes of SEP events are presented. How the parameters related to the parent solar events (i.e. solar flares and coronal mass ejections) can be used to estimate both the probability of occurrence and critical properties (i.e. peak proton flux and/or fluence) of SEP events in the near-Earth environment and beyond, is discussed first. Next, modeling efforts of SEP events that are geared towards operational prediction, particularly focusing on SEP transport effects and multi-spacecraft observations, are reviewed. Furthermore the applicability of higher order multivariate, machine learning and artificial intelligence methods are presented highlighting the particular value and limitations of such advances. Finally, the most current operational approaches in the prediction of SEP events, together with future challenges that need to be addressed by the scientific community, are presented and discussed.
Acknowledgement: This research received funding from the European Union’s Horizon Europe programme under grant agreement No 101135044 (SPEARHEAD). This work was further supported through the ADVISOR - OptimizAtion, DeliVery & Installation of the ASPECS tOol for Space WeatheR research within ISEP project, contract SMS0016862
Speaker information: https://members.noa.gr/atpapaio/
4 Dec 2024 - Prof. Lia Siegelman (Scripps Institution of Oceanography, UC San Diego, USA) -- POSTPONED
"Moist convection and frontogenesis at Jovian high latitudes"
4 Dec 2024 - Prof. Lia Siegelman (Scripps Institution of Oceanography, UC San Diego, USA) -- POSTPONED
"Moist convection and frontogenesis at Jovian high latitudes"
Title: "Moist convection and frontogenesis at Jovian high latitudes"
Abstract: Jupiter’s atmosphere is one of the most turbulent places in the solar system. The Juno spacecraft discovered that Jovian high latitudes host a cluster of large cyclones with diameter of around 5,000 km, each associated with intermediate- (roughly between 500 and 1,500 km) and smaller-scale vortices and filaments of around 100 km. Here, we analyse infrared images from Juno with a high resolution of 10 km. We unveil a dynamical regime associated with a significant energy source of convective origin that peaks at 100 km scales and in which energy gets subsequently transferred upscale to the large circumpolar and polar cyclones. This energy route is expected to enhance the heat transfer from Jupiter’s hot interior to its troposphere and may also be relevant to the Earth’s atmosphere, helping us better understand the dynamics of our own planet. Results also show that the filaments are dynamically active, reminiscent of terrestrial frontogenesis and that Jovian frontogenesis acts in concert with moist convection, with the former mechanism favouring the development of cyclones and the latter the development of anticyclones. This talk highlights the broad range of interacting scales from tens to thousands of kilometres and the diverse physical mechanisms active at Jovian high latitudes.
Title: "Moist convection and frontogenesis at Jovian high latitudes"
Abstract: Jupiter’s atmosphere is one of the most turbulent places in the solar system. The Juno spacecraft discovered that Jovian high latitudes host a cluster of large cyclones with diameter of around 5,000 km, each associated with intermediate- (roughly between 500 and 1,500 km) and smaller-scale vortices and filaments of around 100 km. Here, we analyse infrared images from Juno with a high resolution of 10 km. We unveil a dynamical regime associated with a significant energy source of convective origin that peaks at 100 km scales and in which energy gets subsequently transferred upscale to the large circumpolar and polar cyclones. This energy route is expected to enhance the heat transfer from Jupiter’s hot interior to its troposphere and may also be relevant to the Earth’s atmosphere, helping us better understand the dynamics of our own planet. Results also show that the filaments are dynamically active, reminiscent of terrestrial frontogenesis and that Jovian frontogenesis acts in concert with moist convection, with the former mechanism favouring the development of cyclones and the latter the development of anticyclones. This talk highlights the broad range of interacting scales from tens to thousands of kilometres and the diverse physical mechanisms active at Jovian high latitudes.
Speaker information: https://lsiegelman.scrippsprofiles.ucsd.edu/
18 Dec 2024 - Dr. Lydia Makrygianni (Lancaster University, UK) ** in person**
"Observations of TDEs and Other Nuclear Transients"
18 Dec 2024 - Dr. Lydia Makrygianni (Lancaster University, UK) ** in person**
"Observations of TDEs and Other Nuclear Transients"
Title: Observations of TDEs and Other Nuclear Transients
Abstract: Supermassive Black Holes (SMBHs) at the centres of massive galaxies have been studied for decades, yet many questions regarding their demographics, formation, and evolution remain open. In the case of quiescent galaxies, which comprise the vast majority of the galaxy population in the local universe, short-lived active phases have been attributed to Tidal Disruption Events (TDEs). Active SMBHs (∼10% of all SMBHs in the local Universe), i.e. those steadily accreting material from their surroundings, typically vary in optical flux at the few tens of per cent level. However, recently, unusual activity has been observed in active galactic nuclei (AGN), such as extreme variability, changing-look AGN, and AGN that show atypical emission lines in their spectra. All these phenomena challenge models that attempt to explain the accretion physics and growth of SMBHs. With this talk I aim to present recent advances that have been made in understanding TDEs, make connections to related astrophysical phenomena, and elucidate the most outstanding questions in TDE and other nuclear transient theory and observation. We will also explore how current and new facilities offer a big opportunity for new discoveries and the challenges that are emerging.
20 Dec 2024 - Dr. Stella Boula (INAF Osservatorio Astronomico di Brera, Italy) ** in person**
"Recollimation instabilities and their role in shaping MHD jets"
20 Dec 2024 - Dr. Stella Boula (INAF Osservatorio Astronomico di Brera, Italy) ** in person**
"Recollimation instabilities and their role in shaping MHD jets"
Title: Recollimation instabilities and their role in shaping MHD jets
Abstract: Understanding the structure and dynamics of active galactic nucleus (AGN) jets remains a fundamental challenge in astrophysics. Relativistic magnetohydrodynamical (RMHD) simulations have become invaluable in probing these jets' behavior and emission mechanisms. Recent studies highlight the potential of instabilities downstream of recollimation shocks, where turbulence and shocks can accelerate particles to high energies, potentially explaining the extreme variability observed in high-energy peaked blazars. However, strong magnetic fields may suppress these instabilities, leaving their exact nature and influence an open question. In this work, we explore the development and impact of instabilities downstream of recollimation shocks in AGN jets. Using high-resolution 2D and 3D simulations, we take an initial step toward advanced RMHD modeling with the PLUTO code1. Our findings aim to improve the understanding of AGN jets' non-thermal emission, shedding light on their complex dynamics.
15 Jan 2025 - Dr. Johannes Buchner (Max Planck Institute for Extraterrestrial Physics (MPE), Germany)
"Nuclei ignite! Opening a new type of galaxy evolution studies"
15 Jan 2025 - Dr. Johannes Buchner (Max Planck Institute for Extraterrestrial Physics (MPE), Germany)
"Nuclei ignite! Opening a new type of galaxy evolution studies"
Title: "Nuclei ignite! Opening a new type of galaxy evolution studies"
Abstract: TBA
Title: "Nuclei ignite! Opening a new type of galaxy evolution studies"
Abstract: TBA
Speaker information: https://astrost.at/istics/
22 Jan 2025 - Dr. Francesca Calore (CNRS-LAPTh, Annecy, France )
"The enigmatic gamma-ray sky: Clues, puzzles and breakthroughs"
22 Jan 2025 - Dr. Francesca Calore (CNRS-LAPTh, Annecy, France )
"The enigmatic gamma-ray sky: Clues, puzzles and breakthroughs"
Title: The enigmatic gamma-ray sky: Clues, puzzles and breakthroughs
Abstract: In this presentation, I will provide an overview of the gamma-ray sky, as revealed by over a decade of observations from the Fermi Large Area Telescope (LAT). I will explore the key components of the sky composition, highlighting recent advances in our understanding of diffuse and point-source emissions, and delving into the complexities of the inner Galaxy. In particular, I will focus on a localised excess of GeV gamma rays near the Galactic Center, the so-called Galactic centre GeV excess, which remains a subject of intense scrutiny with proposed explanations ranging from unresolved populations of millisecond pulsars to signals from dark matter annihilation. By examining the latest observational data and theoretical interpretations, I will discuss the challenges in deciphering the origin of this excess and future prospects for unravelling its nature.
Speaker information: https://francescacalore.wordpress.com/
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