15.01.2026

TBD

Joint Journal Club

TBD -------------------------------------------------------------------------------------------------------------------------------------------------------- Meeting ID: 86081722826 Password: 9833 Scheduled time: 15/01/2026 10:30 CET (09:30 UTC) Duration: 120 minutes Meeting link: https://us02web.zoom.us/j/86081722826?pwd=4szYdJKahhMatLXcDrqyuMMHIeHnnP.1 --------------------------------------------------------------------------------------------------------------------------------------------------------

04.02.2026

Alessandro Ignesti

Unveiling the physics of ram pressure stripping: New insights from GASP

Jellyfish galaxies, characterised by long filaments of stripped interstellar medium extending from their disks, are prime laboratories to study the results of ram pressure stripping in galaxy clusters and to explore the astrophysics of galaxies under extreme conditions. I will present a series of recent results in this field made by the GASP (GAs Stripping Phenomena in galaxies with MUSE) team based on a multi-wavelength survey of ram-pressure-stripped galaxies. Using a combination of LOFAR and MUSE observations, we have explored how the non-thermal components of the interstellar medium, namely magnetic fields and cosmic rays, evolve under the influence of ram pressure. First, I will show how we can use the stripped ionised plasma tails to probe the intracluster medium microphysics. Then I will provide an overview of how LOFAR has changed our understanding of the non-thermal radio emission observed in these galaxies and how the extraplanar magnetic field can regulate the interplay between the stripped interstellar medium and the surrounding intracluster medium. Finally, I will discuss the future perspectives in the upcoming SKA era.

09.03.2026

Taj Jankovič

Radiation-hydrodynamics of star–disc collisions for quasi-periodic eruptions

Quasi-periodic eruptions (QPEs) are recently discovered transients of unknown nature occurring near supermassive black holes, which feature bright X-ray bursts separated by hours to days. A promising model for QPEs is the star-disc collisions model, where a star repeatedly interacts with an accretion disc around a black hole, creating shocks that expel dense outflows of gas from which radiation emerges. We investigate the dynamics of the star-disc collisions, the properties of the outflows, and the resulting radiation signatures. Our study focuses on the generic case where the star remains unperturbed by the collision and the stellar crossing time through the disc is sufficiently long for shocked gas to flow around the star. We performed a three-dimensional radiation-hydrodynamics simulation of the star-disc collision. The star was modeled as a solid, spherical body, and the interaction was simulated for a small, local section of the accretion disc. We found that star–disc collisions generate a nearly paraboloidal bow shock. The heating of gas is not confined to the column of gas directly ahead of the star but also extends laterally as the shock front expands sideways while traveling with the star. As the star crosses the disc, it injects momentum preferentially along its direction of motion, leading to an asymmetric redistribution of energy and momentum. As a result, two outflows emerge on opposite sides of the disc with different properties: the forward outflow expands faster, contains more mass, carries more energy, and is about twice as luminous as the backward outflow. Our findings suggest that the asymmetry in outflow properties and luminosity arises naturally from the collision dynamics, offering a possible explanation for the alternating "strong–weak" flare patterns observed in several QPE sources.

19.03.2026

Shilpa Sarkar & Richard Wunsch

Joint Journal Club (Sporilov and via Zoom)

>> From the Stellar department, Shilpa Sarkar will present the paper: "Global Structure of Accretion Flows in Sgr A*": https://arxiv.org/abs/2603.03996 =================================================================================== >> From the Galaxies department, Richard Wunsch will present the paper: "The PHANGS-MUSE/HST-Hα nebulae catalogue: Parsec-scale resolved structure, physical conditions, and stellar associations across nearby galaxies" =================================================================================== Meeting ID: 81888620962 Password: 9540 Link: https://us02web.zoom.us/j/81888620962?pwd=zTuhRAC1h6cZeZEZ6bbVjXCyE6KodJ.1 ---------------------------------------------------------------------------------------------------------------------------------------------------

01.04.2026

Nushkia Chamba

Across the Faint Universe: How Deep Images Reveal The History of Galaxies Big and Small

As galaxies form and evolve in the Universe, they leave behind a complex trail of ultra-faint stars and gas in their outskirts. This faint material holds clues to the growth and accretion history of galaxies. In this colloquium, we present some of the deepest images of the faint universe, of dwarf and massive galaxies, as seen in X-ray, optical and radio wavelengths. We discuss how these images help us understand the key physical and environmental processes such as star formation, feedback and mergers that drive the growth of galaxies big and small. These results demonstrate the importance of preserving low surface brightness structure in the next generation of surveys from Euclid, Rubin-LSST, Roman and SKA in order to further our understanding of galaxies across the Universe.

08.04.2026

Lýdia Štofanová

From atoms to the cosmos:

Our Universe, more specifically, the warm-hot intergalactic medium in the cosmic web filaments, the intra-cluster medium of galaxy clusters, and the circum-galactic medium around individual galaxies is full of such metals. By studying the medium of these massive astrophysical objects through spectroscopy, and by studying the impact of different feedback processes on the metal transport on various physical scales, we can get closer to the understanding of the origin and evolution of metals in some of the most massive objects in our Universe. In this talk I will give an overview of my Ph.D. thesis, which focused on the spectroscopy of the cosmic web (filaments and galaxy clusters) with current and future X-ray telescopes like e.g. NewAthena. I will show that future X-ray micro-calorimeter missions will be sensitive to effects that have not yet been detected before, like for example observing WHIM in absorption against bright cool-core clusters. I will briefly mention the importance of updating the atomic databases and plasma codes in the X-ray regime. In the past two years, I shifted my career towards the space industry, more specifically, over time I got more involved in the QUVIK mission - the very first Czech-led space telescope for which I recently accepted a role of the main project manager. I will briefly mention updates about QUVIK. I will also briefly talk about the new science public outreach activities that we are preparing in Brno together with my colleagues.

14.04.2026

Lýdia Štofanová

From atoms to the cosmos

Our Universe, more specifically, the warm-hot intergalactic medium in the cosmic web filaments, the intra-cluster medium of galaxy clusters, and the circum-galactic medium around individual galaxies is full of such metals. By studying the medium of these massive astrophysical objects through spectroscopy, and by studying the impact of different feedback processes on the metal transport on various physical scales, we can get closer to the understanding of the origin and evolution of metals in some of the most massive objects in our Universe. In this talk I will give an overview of my Ph.D. thesis, which focused on the spectroscopy of the cosmic web (filaments and galaxy clusters) with current and future X-ray telescopes like e.g. NewAthena. I will show that future X-ray micro-calorimeter missions will be sensitive to effects that have not yet been detected before, like for example observing WHIM in absorption against bright cool-core clusters. I will briefly mention the importance of updating the atomic databases and plasma codes in the X-ray regime. In the past two years, I shifted my career towards the space industry, more specifically, over time I got more involved in the QUVIK mission - the very first Czech-led space telescope for which I recently accepted a role of the main project manager. I will briefly mention updates about QUVIK. I will also briefly talk about the new science public outreach activities that we are preparing in Brno together with my colleagues.

17.04.2026

Masafumi Imai et al.

Connecting Radio Groups: Astronomy, Solar System Science, and Outreach

An informal meeting of the radio groups at ASU and the Institute of Atmospheric Physics to discuss the use of radio observations in astronomy and space science, including solar radio research and Jovian science, the involvement in the international infrastructures LOFAR, ALMA, as well as local radio instrumentation in Ondřejov. The seminar will also explore the outreach potential of portable radio antennas, including an LWA antenna and a CubeSat cardboard Yagi antenna, and discuss possibilities for future collaboration.

17.04.2026

Eliška Kleinová

Interpreting an Accretion Disk Look-Alike in JWST Imaging

Deep imaging with the James Webb Space Telescope is revealing a growing number of faint and morphologically complex sources whose nature is not immediately clear. In this talk, we focus on a peculiar extended object identified in the field of WR-124, which at first glance exhibits an unusually elongated structure reminiscent of an accretion disk around a supermassive black hole. We analyze multi-wavelength imaging from the MIRI and NIRCam instruments and perform aperture photometry to estimate the source brightness and angular size (~1 × 1.5 arcsec). Using spectral energy distribution fitting, we constrain its physical properties and find a likely redshift of z ≈ 0.8. Based on the combined photometric and morphological analysis, we consider possible interpretations of the object, in particular a galaxy merger or a gravitational lensing configuration. We present the methodology used to derive these constraints and discuss the limitations of the current data in distinguishing between these scenarios.

24.04.2026

Mattia Pacicco

Magnetised bubbles across scales: from supernova remnants to the Local Bubble - with 3D MHD simulations

Magnetised bubbles pervade the interstellar medium across a vast range of scales, from individual supernova remnants (SNRs) to the superbubbles they collectively inflate. We present two complementary 3D magnetohydrodynamic studies tracing this hierarchy from its smallest building blocks to its most prominent local example. We simulate SNRs expanding into a non-homogeneous, magnetised two-phase medium, obtaining complex magnetic field configurations in their interiors. Strongly magnetised remnants develop magnetically confined hot cavities surrounded by a diffuse magnetised halo, and remain orders of magnitude more X-ray luminous than their weakly magnetised counterparts. We then extend our study to larger scales, simulating the Local Bubble: a superbubble encasing the Solar neighbourhood, whose expansion has been driven by numerous supernovae. We characterise its turbulent interior magnetic field and its amplification in the shell, while also modelling neighbouring superbubbles and SNRs within 1 kpc of the Sun. Together, these parsec- to kiloparsec-scale frameworks give us insights on the coupling between magnetic fields and stellar feedback, from individual remnants to the large-scale cavities structuring the local interstellar medium.

28.05.2026

Michalis Kourniotis and Alessandro Ignesti

Joint Journal Club (Sporilov and via Zoom)

>> From the Stellar Department Michalis Kourniotis will present the paper : "The dramatic transition of the extreme red supergiant WOH G64 to a yellow hypergiant", https://www.nature.com/articles/s41550-026-02789-7 >> From the GPS Department Alessandro Ignesti will present the paper : "The Impact of Ram Pressure on the Radio Spectral Index and Magnetic Field of NGC 4522: A High-resolution VLA Continuum Study", https://ui.adsabs.harvard.edu/abs/2026ApJ...999..116C/abstract ========================================================================== Meeting ID: 88035534277 Password: 7409 Link: https://us02web.zoom.us/j/88035534277?pwd=vy3qSoUtYcJU69bYTdsf91A0pK8Twb.1 Scheduled time: 28/05/2026 10:30 CEST (08:30 UTC) ==========================================================================

28.05.2026

Samik Mitra

Importance of low angular momentum magnetised accretion flows around Sgr A*

Accretion onto Sgr A* is often discussed in terms of SANE and MAD models, where the flow is described as a turbulent, rotationally supported magnetised disk. In this talk, I will instead focus on a complementary semi-analytical picture: low angular momentum magnetised accretion. In this regime, the gas has too little angular momentum to form a Keplerian disk, so the dynamics are dominated by radial infall, weak rotation, magnetic pressure, and gravity. Even modest angular momentum can create a centrifugal barrier close to the black hole, where the supersonic inflow may undergo shock formation, producing a hot, compressed post-shock region. This gives the flow a more quasi-spherical and transonic character, distinct from the disk-like SANE/MAD paradigm. Using semi-analytical models, one can follow how the shock location, compression ratio, velocity, density, and magnetic-field strength depend on the flow parameters. I will discuss how such low angular momentum solutions provide a physically motivated framework for understanding magnetic-field amplification, dissipation, and possible flare-like activity near Sgr A*, and why they may be important alongside fully numerical GRMHD disk models.