2023 Spring Schedule
8 March 2023 - Dr. John Antoniadis (Institute for Astrophysics, FORTH)
Title: ARGOS: a Next-Generation Radio Telescope for Multi-Messenger Astrophysics
Abstract: Astronomy is being transformed by multi-messenger surveys performed with instruments capable of searching the sky with high speed and sensitivity, while delivering science-ready datasets to the community. While radio astronomy is not yet fully participating in this revolution, it is clear that an instrument following the same philosophy is not only urgent but inevitable. ARGOS is a concept for a leading-edge, low-cost, sustainable European astronomical facility that will finally realise this ambition, directly addressing multiple fundamental scientific questions, from the nature of dark matter and dark energy to the origin of fast radio bursts and the properties of extreme gravity, thereby satisfying urgent needs of the community. ARGOS will enable, for the first time, continuous wide-field monitoring of the sky at centimetre wavelengths, while publicly distributing science-ready data and alerts in real time.
ARGOS recently entered a three-year detailed design phase, which will prepare the subsequent rapid implementation of this leading-edge public radio facility on European grounds, and ensure its optimal integration into the network of existing and future international astronomical infrastructures. This will be achieved following a systems-engineering approach that will integrate technical studies, community groundwork, and prototyping, as well as quantitative cost-to-benefit analysis, and assess socioeconomic impact, sustainability, technological readiness, and innovation needs.
In this talk, I will describe the project and its main science and engineering objectives, as well as ARGOS-pathfinder, a 16-dish prototype that will be installed at Skinanas as part of the project.
15 March 2023 - Dr. Manos Zapartas (National Observatory of Athens) **hybrid**
Title: Massive binary progenitors of core-collapse supernovae
Abstract: I will talk about core-collapse supernovae explosions, which mark the end of the life of massive stars, but for which the origin and evolution of their progenitors is not yet fully understood. Focusing firstly on Hydrogen-poor supernovae (e.g. Type Ib, Ic, IIb) that have lost their hydrogen-rich envelope prior to explosion, I will discuss the evidence against single, Wolf-Rayet progenitors, taking into account more specifically the possibility that many of these stars do not explode. As most young massive stars are found in binary systems, the most probable alternative scenario is that most hydrogen-poor progenitors get stripped due to mass transfer. I will emphasize on the constantly increasing observational sample of the surviving binary companions next to these explosions, and compare them with population synthesis predictions from simplified and detailed binary models with POSYDON. In the second part, I will focus on Hydrogen-rich, Type II SNe, and the effect that binarity and wind mass loss have on the time, the location, the inferred mass of the progenitor and the "Red Supergiant problem" of observed lack of luminous RSGs progenitors for them. I will show a way to potentially identify a binary progenitor of a nearby Type II SN, based on combining results of different observational methods, implemented a case study.
22 March 2023 - Prof. Dr. Andreas Eckart (University of Cologne, MPIfR Bonn) **hybrid**
Title: Update on Aspects in Galactic Center Research
Abstract: We summarize recent research results on the radiation mechanism of the Super Massive Black Hole (SMBH) candidate SgrA* and ask the question if there are Intermediate Mass Black Hole (IMBH) candidates in the central stellar cluster. Furthermore we give an update on the most recent high velocity stars in the central arcsecond - that are closest to SgrA*. Here we concentrate on the high velocity star cluster dynamics and on the 4711+ stars with orbital time scales down to 4 years only.
24 March 2023 - Dr. Georgios Nicolaou (Mullard Space Science Laboratory, University College London) **in person**
Title: Solar Orbiter: Understanding the mechanisms of the Sun
Abstract: Solar Orbiter is a mission by ESA, with strong participation by NASA, observing the Sun using in-situ and remote sensing instruments. Solar Orbiter is the first spacecraft obtaining high resolution images of the Sun from ~0.3 AU. At the same time, state-of-the-art instruments are monitoring the plasma and electromagnetic fields at the spacecraft location. The combination of the images of the Sun in different depths and in-situ observations, is crucial in understanding the complicated mechanisms of the Sun and how the Sun controls the entire Heliosphere. In this talk, we will focus on the Solar Wind plasma observations by Solar Orbiter. We will explain how the several plasma instruments on-board the spacecraft can monitor the Solar Wind species. We will then demonstrate how the plasma observations are analyzed to estimate the plasma bulk properties, which we need to understand physical processes in space. Finally, we will show some examples of the latest measurements in dynamical plasma structures, such as Interplanetary Coronal Mass Ejections (ICMEs), Interplanetary Shocks and more.
5 April 2023 - Dr. Rafael Alves-Batista (Universidade Autónoma de Madrid)
Title: A multimessenger view of the ultra-high-energy universe
Abstract: The origins of the most energetic particles in the Universe has been a long-standing puzzle. In the quest to identify their sources, it is essential to understand how these particles are accelerated, how they can escape the sites wherein they are produced, and which roads they can take on their journey to Earth. The multimessenger framework has proven a powerful tool for exploring the Universe at these extreme energies. In this talk I will focus on the triad of (ultra-)high-energy messengers: cosmic rays, neutrinos, and gamma rays. I will first briefly discuss the state of affairs in this field, reviewing some key theoretical developments and experimental results. I will then present the ingredients required for building theoretical models to interpret the measurements. Emphasis will be given in modelling the propagation of these messengers, including their interactions with matter and radiation fields, and with the poorly-understood cosmic magnetic fields. Finally, I will discuss the prospects for building a unified self-consistent model of the Universe at ultra-high energies and the implications such a model would have for astrophysics, cosmology, and fundamental physics.
26 April 2023 - Prof. Samuel Lander (University of East Anglia) **in person**
Title: What makes a magnetar?
Abstract: A magnetar is a neutron star with a strong magnetic field, whose characteristic emission ranges from short X-ray bursts up to giant gamma-ray flares, but also includes regular and bursting radio emission. Much of this behaviour is likely to be related to seismic activity from the star’s solid crust. These stars are probably the only environment in the Universe where phenomena from all branches of modern physics are involved. This talk will survey neutron-star/magnetar magnetic fields, and focus on two key questions: what processes could generate these intense magnetic fields, and how seismic activity might lead to the powering of magnetar bursts.
3 May 2023 - Dr. Maria Charisi (Vanderbilt University)
Title: Searching for supermassive black hole binaries in the era of multi-messenger Astronomy
Abstract: Supermassive black holes (SMBHs) with mass of a million to ten billion times the mass of the sun reside in the center of most galaxies. Additionally, galaxies merge frequently to form bigger galaxies. This naturally leads to galaxies with two SMBHs, which progressively move to smaller and smaller separations and form gravitationally bound binaries. Even though supermassive black hole binaries (SMBHBs) should be common, they remain a missing piece in the puzzle of galaxy formation. SMBHBs can be detected from their bright electromagnetic (EM) emission as quasars with periodic variability. I will describe recent EM searches for SMBHBs that have revealed ~250 promising candidates and prospects for future detections in the massive dataset of the upcoming Rubin Observatory. SMBHBs are also promising sources of low-frequency, soon to be detected by pulsar timing arrays, making them exceptional targets for multi-messenger observations. I will present exciting recent results from the North American Nanohertz Observatory for Gravitational waves (NANOGrav) collaboration, which may provide the first hints of a low-frequency GW background from SMBHBs. Finally, I will discuss multi-messenger constraints on SMBHBs from recent NANOGrav upper limits, along with the prospects for multi-messenger discovery.
17 May 2023 - Dr. Ekaterina Sokolova-Lapa (University of Erlangen-Nuremberg) **in person**
Title: Modeling radiative transfer in the vicinity of accreting neutron stars
Abstract: Neutron stars in binary systems with an early-type (OB) companion typically posses strong magnetic fields of ~10^12 G. These fields strongly affect accretion phenomena that can occur in a close binary. Approaching the neutron star, the accretion flow couples to the magnetic field and is channeled to the magnetic poles. Braking of the flow near the neutron star surface is associated with an enormous energy release, which results in intense X-ray radiation, which appears to pulsate for the remote observer due to the rotation of the neutron star. The spectra from these accreting X-ray pulsars typically show a power-law-like shape with high-energy cutoff and often contain wide absorption features imposed by the strong magnetic field, which are known as cyclotron lines. In this talk, I will present the current state of theoretical modeling of the emission from accreting X-ray pulsars, along with the most recent observational puzzles, that challenge the traditional view on the spectral formation. I will discuss the ways to simulate radiative transfer in highly magnetized plasma and the possible influence of the polarized vacuum on the shaping of the observed spectra. Finally, I will demonstrate how the angle-, energy, and polarization-dependent radiative transfer in combination with relativistic ray tracing allows to access fundamental parameters, such as the strength of the polar magnetic field, the location of the magnetic poles, and the viewing angle to the rotational axis of the neutron star.
24 May 2023 - Prof. Maria Weber (Delta State University)
Title: How Suns get their Spots: What we know and what we don't
Abstract: Starspots are manifestations of a star’s internal magnetic processes. However, even for our own Sun, there are still many uncertainties about the complex mechanisms that give the Sun its spots. Within the context of magnetic flux emergence in the Sun, I will discuss what we know and what we don’t about how active region magnetism is generated and rises through the solar interior to produce sunspot observables. I will also discuss our work to establish links between dynamo-generated magnetic fields, shearing and fluid motions, and observations of starspots in solar-like stars down to fully convective M dwarfs.
31 May 2023 - Prof. Lia Athanassoula (Laboratoire d'astrophysique de Marseille)
Title: Bars and their effect on galaxy evolution
Abstract: Bars are elongated features in the central part of galactic discs. With the torques they exert, they redistribute the angular momentum within the galaxy, and drive its evolution. Using state-of-the-art numerical simulations, we will discuss these processes and see how they affect the morphology and kinematics of the gaseous and the stellar component, as well as the effect of the dark matter halo on this evolution