SFB Colloquium
Prof. Robin Garrod	SCHEDULED

University of Virginia

The interstellar medium provides an enormous laboratory for the exploration of chemistry of various kinds. Some of the most molecule-rich interstellar objects - known as "hot molecular cores" - are accretions of warm gas and dust that surround young protostars, which ultimately evolve into high-mass stellar systems. Along with their low-mass (solar-type) analogs, "hot corinos", they are characterized by rich rotational emission spectra that exhibit a wealth of organic molecules of varying degrees of complexity. But the formation of these "hot" (>100 K), gas-phase molecules is closely related to an earlier stage of chemistry that occurs on the surfaces of microscopic dust grains at much lower temperatures. Recent observational, experimental and modeling evidence indicates that some of the most complex molecules that we detect in highly evolved protostellar systems may have a much earlier origin than previously thought. Here I will present new modeling treatments that allow us to trace the continuum of hot and cold chemistry involving interstellar organics. I will also demonstrate some initial results from new coupled radiation hydrodynamics and gas-grain chemical modeling of hot core/corino systems, and our efforts to simulate observations of their molecular line emission.

	Special Colloquium
Dr. Shafqat Riaz	SCHEDULED

University of Tuebingen

Abstract: Various approaches, including gravitational waves (GWs), very long baseline interferometry (VLBI), and X-ray data from accreting black holes (BHs), can probe different aspects of gravity in the strong curvature regime, where deviations from Einstein's General Relativity (GR) are expected to be most pronounced. These methods are not only complementary but also essential for testing gravity theories across diverse domains. X-ray reflection spectroscopy, a technique for analyzing reflection data from accreting BHs, has advanced significantly over the past few decades. It has been applied to both stellar-mass and supermassive black holes (SMBHs), with current X-ray telescopes providing the high-quality data necessary to constrain potential deviations from GR. Upcoming X-ray missions, such as Athena, HEXP, and eXTP, are expected to deliver data of unprecedented quality, enabling more rigorous theory-independent and theory-dependent tests of gravity. In this talk, I will present results from GR tests conducted using X-ray reflection spectroscopy and discuss the potential of future missions to further advance these studies.

	Special Colloquium
Dr. Efthalia Traianou	SCHEDULED

Instituto de Astrofísica de Andalucía-CSIC, Granada

OJ 287 is one of the most fascinating blazars, believed to host a binary supermassive black hole system and known for its rich history of multi-wavelength variability. In this talk, I will present high-resolution 22 GHz space VLBI observations of OJ 287 from RadioAstron (April 2016), offering a unique view of its jet structure and magnetic field topology at sub-milliarcsecond scales. Our imaging reveals a bent jet morphology, significantly more extended than seen in previous years. Using regularized maximum-likelihood imaging and polarimetric analysis, we observe a transition in the magnetic field from a toroidal-dominated core to a helical structure downstream, indicating an evolving jet. Additionally, model-fitting suggests the emergence of a new component, likely linked to the December 2015 optical outburst and the secondary black hole's passage through the primary's accretion disk.

	Main Colloquium
Dr. Stella Ocker	SCHEDULED

Carnegie-Caltech Brinson Fellow

The time has come for a new electron density model of the Milky Way. Galactic electron density models describe the multi-component, multi-scale structure of the ionized interstellar medium (ISM). These models are routinely used to predict the distances of radio sources lacking independent distance measures, in addition to forward modeling the dispersion and scattering of pulsars, fast radio bursts (FRBs), active galactic nuclei, and masers. In this talk I will discuss the developments motivating construction of a new electron density model, and some key puzzles that face our understanding of multi-scale electron density structure in our Galaxy. Unlike previous models, large-scale surveys of the ionized ISM are being actively folded into the model construction. Specific case studies will be discussed to demonstrate how characterization of the Galactic electron density affects our understanding of extragalactic FRBs and their use as cosmic probes.