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.