Spring 2024
3 Apr 2024 - Prof. Ilya Usoskin (University of Oulu, Finland)
"Cosmic rays at Earth"
"Cosmic rays at Earth"
Title: Cosmic rays at Earth
Abstract: The lecture "Cosmic Ray at Earth" presents a brief overview of the history of cosmic ray discovery and study. Cosmic rays were discovered in 1912 through the effect of atmospheric ionization and soon became an important object and subject of intense research. The modern paradigm of what cosmic rays are, where and how they are formed and what effects they cause on Earth will be presented. The following topics will be touched on: cosmic ray acceleration, energy spectrum and composition; measurements of cosmic rays; Heliospheric modulation; solar energetic particles including extreme solar events; terrestrial effect of cosmic rays.
17 Apr 2024 - Prof. Sergei Klioner (Technische Universität Dresden, Germany)
"The adventure of astrometry with Gaia"
"The adventure of astrometry with Gaia"
Title: The adventure of astrometry with Gaia
Abstract: Gaia astrometry gradually has become a regular tool in various fields of astronomical research. Basic principles of astrometric measurements by the ESA's space telescope Gaia will be presented. I will review the content of astrometric data published by Gaia and briefly explain its quality indicators. The role of quasars for both derivation and verification of Gaia astrometry will be stressed. I will then discuss a less standard side of Gaia astrometry: the so-called "global" astrometric effects. Those effects are independent of the nature of the observed sources and related either to Gaia as an observer or to the underlying physical laws needed to formulate the model of observations. Examples here are the effects of acceleration of the solar system, those of gravitational waves etc.
Abstract: Gaia astrometry gradually has become a regular tool in various fields of astronomical research. Basic principles of astrometric measurements by the ESA's space telescope Gaia will be presented. I will review the content of astrometric data published by Gaia and briefly explain its quality indicators. The role of quasars for both derivation and verification of Gaia astrometry will be stressed. I will then discuss a less standard side of Gaia astrometry: the so-called "global" astrometric effects. Those effects are independent of the nature of the observed sources and related either to Gaia as an observer or to the underlying physical laws needed to formulate the model of observations. Examples here are the effects of acceleration of the solar system, those of gravitational waves etc.
24 Apr 2024 - Dr. Panos Patsis (Academy of Athens) ** in person **
"Why should we care about how fast spiral arms and bars of galaxies rotate? "
Title: Why should we care about how fast spiral arms and bars of galaxies rotate?
- Understanding the significance of determining their pattern speeds.
Abstract: TBA
15 May 2024 - Prof. Emanuele Berti (Johns Hopkins University, USA)
"Nonlinear black hole spectroscopy"
Title: Nonlinear black hole spectroscopy
Abstract: According to general relativity, the remnant of a binary black hole merger is a perturbed Kerr black hole. Perturbed Kerr black holes emit "ringdown" radiation which is well described by a superposition of damped exponentials ("quasinormal modes”), with frequencies and damping times that depend only on the mass and spin of the remnant. The observation of gravitational radiation emitted by black hole mergers might finally provide direct evidence of black holes, just like the 21 cm line identifies interstellar hydrogen. I will review the current status of this "black hole spectroscopy" program. I will focus on: (1) the role of nonlinearities in ringdown modeling, (2) the current observational status of black hole spectroscopy, and (3) future prospects for the observability of nonlinear modes.
Abstract: According to general relativity, the remnant of a binary black hole merger is a perturbed Kerr black hole. Perturbed Kerr black holes emit "ringdown" radiation which is well described by a superposition of damped exponentials ("quasinormal modes”), with frequencies and damping times that depend only on the mass and spin of the remnant. The observation of gravitational radiation emitted by black hole mergers might finally provide direct evidence of black holes, just like the 21 cm line identifies interstellar hydrogen. I will review the current status of this "black hole spectroscopy" program. I will focus on: (1) the role of nonlinearities in ringdown modeling, (2) the current observational status of black hole spectroscopy, and (3) future prospects for the observability of nonlinear modes.
22 May 2024 - Prof. Manuela Temmer (University of Graz, Austria)
"The structured heliosphere – solar wind, transient disturbances and their solar origin"
"The structured heliosphere – solar wind, transient disturbances and their solar origin"
Title: The structured heliosphere – solar wind, transient disturbances and their solar origin
Abstract: The Sun's most dynamic events manifest as coronal mass ejections (CMEs) and flares. CMEs consist of enormous clouds of magnetized plasma hurtling at speeds of up to a few thousand kilometers per second. These can traverse the distance between the Sun and Earth in less than a day, potentially triggering significant geomagnetic disturbances on our planet, known as Space Weather. CMEs travel within the ambient flow of solar wind, which itself is structured by the interaction between slow and fast wind streams. These different solar wind streams, generating stream interaction regions (SIRs), can induce geomagnetic storms, often recurring periodically. With the recent period of high solar activity, particularly evident during the "May 2024" solar storms, there is an increased interest in better understanding the impact of solar events on Earth. Understanding the underlying physical processes governing the interplay between solar wind flow and CMEs is crucial for refining models and enhancing the reliability of forecasts. The talk will cover the phenomena of CMEs and flares, their propagation through interplanetary space in relation to the background solar wind.
29 May 2024 - Dr. Yuri Cavecchi (University of Barcelona, Spain)
"Thermonuclear Type I Bursts and the Physics of Neutron Stars"
"Thermonuclear Type I Bursts and the Physics of Neutron Stars"
Title: "Thermonuclear Type I Bursts and the Physics of Neutron Stars"
Abstract: Neutron stars are born in the aftermath of supernova stellar explosions. They enclose the mass of one or two suns within only ten kilometres, so that their gravity is so high that general relativistic effects become important in their proximity, affecting the space time and light propagation near their surface. Due to their compactness, their interior reaches density unattainable on earth. Their matters can be superfluid, superconductor and in their core even free quarks may appear.
Abstract: Neutron stars are born in the aftermath of supernova stellar explosions. They enclose the mass of one or two suns within only ten kilometres, so that their gravity is so high that general relativistic effects become important in their proximity, affecting the space time and light propagation near their surface. Due to their compactness, their interior reaches density unattainable on earth. Their matters can be superfluid, superconductor and in their core even free quarks may appear.
When they are in orbit with a companion star, they can capture the outer layers of the latter. This new matter can burn unstably on the surface of the neutron stars and explode in bright X-ray flashes called the type I bursts.
In this talk I will show how modelling the magnetohydrodynamics of the flame during the type I bursts gives us a window on properties of the neutron stars such as their magnetic fields or their interior physics, which has also connections to gravitational waves.
I will also discuss how these simulations can give us information relevant to nuclear physics, related both to astronomical events such as binary mergers and experiments on earth.
12 Jun 2024 - Dr. Elias Roussos (Max Planck Institute for Solar System Research, Germany)
"Measuring Jupiter’s extreme particle radiation environment: challenges and solutions"
"Measuring Jupiter’s extreme particle radiation environment: challenges and solutions"
Title: Measuring Jupiter’s extreme particle radiation environment: challenges and solutions
Abstract: Jupiter is a planet of superlatives and its magnetosphere is no exception to that. The planet’s giant magnetosphere, generated by a magnetic field 20000 times stronger than that of the Earth, acts also as a very powerful charged particle accelerator, giving rise to the most hazardous particle radiation environment in our solar system: Jupiter’s radiation belts. The radiation belts of Jupiter trap a diverse mix of particles species (electrons, protons, heavy ions) with energies characteristic for galactic cosmic rays, albeit at intensities many orders of magnitude higher than the latter. How these radiation belts end up being so energetic and so intense is a decades-long reigning mystery, in part because their measurement presents us with numerous scientific and technical challenges. What our existing measurements indicate is that the fundamental space physics processes and their synergies that operate at Jupiter’s belts, such as particle acceleration, transport and loss, are unparalleled in our solar system and could offer us insights into the dynamics of astrophysical, extrasolar magnetospheres that we can only probe remotely. In this presentation I will briefly introduce what makes Jupiter’s radiation belts so unique and the current state of our understanding, before focusing on how future missions, instruments and measurement strategies will help us probe this unique system in depth.
26 Jun 2024 - Prof. Bart Ripperda (Canadian Institute for Theoretical Astrophysics at the University of Toronto, Canada) ** in person**
"How black holes accrete and eject"
"How black holes accrete and eject"
Title: "How black holes accrete and eject."
Abstract: Astrophysical black holes are surrounded by accretion disks, jets, and coronae consisting of magnetized relativistic plasma. They produce observable high-energy radiation from nearby the event horizon and it is currently unclear how this emission is exactly produced. The radiation typically has a non-thermal component, implying a power-law distribution of emitting relativistic electrons. Magnetic reconnection and plasma turbulence are viable mechanisms to tap the large reservoir of magnetic energy in these systems and accelerate electrons to extreme energies. The accelerated electrons can then emit high-energy photons that themselves may strongly interact with the plasma, rendering a highly nonlinear system. Modeling these systems necessitates a combination of magnetohydrodynamic models to capture the global dynamics of the formation of dissipation regions, and a kinetic treatment of plasma processes that are responsible for particle acceleration, quantum electrodynamics effects like pair creation and annihilation, and radiation. I will present novel studies of accreting black holes and how they radiate in regions close to black hole event horizon, using both first-principles general relativistic kinetic particle-in-cell simulations and global large-scale three-dimensional magnetohydrodynamics models. With a combination of models, I determine where and how dissipation of magnetic energy occurs, what kind of emission signatures are typically produced, and what they can teach us about the nature of black holes.
Abstract: Astrophysical black holes are surrounded by accretion disks, jets, and coronae consisting of magnetized relativistic plasma. They produce observable high-energy radiation from nearby the event horizon and it is currently unclear how this emission is exactly produced. The radiation typically has a non-thermal component, implying a power-law distribution of emitting relativistic electrons. Magnetic reconnection and plasma turbulence are viable mechanisms to tap the large reservoir of magnetic energy in these systems and accelerate electrons to extreme energies. The accelerated electrons can then emit high-energy photons that themselves may strongly interact with the plasma, rendering a highly nonlinear system. Modeling these systems necessitates a combination of magnetohydrodynamic models to capture the global dynamics of the formation of dissipation regions, and a kinetic treatment of plasma processes that are responsible for particle acceleration, quantum electrodynamics effects like pair creation and annihilation, and radiation. I will present novel studies of accreting black holes and how they radiate in regions close to black hole event horizon, using both first-principles general relativistic kinetic particle-in-cell simulations and global large-scale three-dimensional magnetohydrodynamics models. With a combination of models, I determine where and how dissipation of magnetic energy occurs, what kind of emission signatures are typically produced, and what they can teach us about the nature of black holes.