Main Colloquium
Prof. Dr. Claudio Ricci	SCHEDULED

Department of Astronomy, University of Geneva, Switzerland

Accreting supermassive black holes can outshine their host galaxies, yet the physical conditions close to these objects remain difficult to measure. One of the least understood regions is the corona, the hot plasma responsible for much of their X-ray emission. How is this plasma heated, what magnetic fields does it contain, and how does it accelerate particles? Recent observations suggest that millimeter emission could provide a complementary way to address these questions, while also helping us find accreting black holes hidden by gas and dust. In my talk, I will present recent results obtained using high-resolution ALMA observations of nearby active galaxies without powerful radio jets. We detect compact millimeter emission in almost all of these systems and find a tight relationship with their X-ray luminosity, suggesting a close connection between the two emitting regions. Our recent work on more luminous, rapidly accreting black holes reveals stronger millimeter emission than expected from this relation, alongside a close connection with the total power radiated by the accretion flow. I will discuss what these results tell us about how the plasma changes as black holes accrete more rapidly. Observations at several millimeter wavelengths, variations on timescales of days, and polarization measurements provide further clues to where the radiation is produced. Combined with physical models, these measurements allow us to test a coronal origin and investigate the size, magnetic fields, and energetic electron population of the emitting plasma. Finally, I will discuss how millimeter observations could reveal black hole growth in systems so heavily obscured that even their X-ray emission is strongly suppressed.

	Main Colloquium
Prof. Dr. Tim Dietrich	SCHEDULED

Max-Planck-Institut für Gravitationsphysik, Potsdam/Golm

Neutron stars are among the densest known objects, and the merger of two neutron stars is one of the most energetic phenomena known. Interpreting these mergers through their multi-messenger emission requires accurate theoretical models that can be correlated with the observational data. Gravitational-wave models combine ab initio numerical-relativity simulations with analytical waveform approximations, enabling predictions that are both accurate and computationally efficient. Similar modelling strategies can be applied to electromagnetic counterparts, including the kilonova and the gamma-ray burst afterglow. Integrating these components into a unified multi-messenger framework enables the extraction of fundamental physics from observations, leading to tighter constraints on the equation of state of neutron stars, more precise measurements of the Hubble constant, and a better understanding of heavy-element production in the Universe. This colloquium is initiated by the IMPRS students of the MPIfR.