Informal Colloquium
Ahmad Jaradat	SCHEDULED

Institute for Geodesy and Geoinformation, University of Bonn

The topic of this talk is the conception of a broadband radio signal to be emitted by a satellite. Observations of satellites with VLBI are the only suitable method for directly linking the dynamic reference frame of satellite orbits to the celestial reference frame realized by astrometric surveys of active galactic nuclei (AGN). Previous investigations have shown that embedding satellite observations into regular geodetic VLBI sessions can improve the frame-ties between celestial and terrestrial reference frames. For this reason, the artificial signal received from the satellite should be similar to the radio emission from an AGN as observed from the surface of the Earth. I will present equipment that could, e.g., serve as an additional payload for a Global Navigation Satellite System (GNSS). Results from simulations will be presented. Legal and technical feasibilty aspects will be discussed.

	Main Colloquium
Dr. Tanja Hinderer	SCHEDULED

University of Amsterdam, the Netherlands

The recent detections of gravitational waves from merging black holes and neutron stars have established gravitational waves as a new cosmological messenger and opened remarkable opportunities for probing the physics of gravity and matter in unexplored regimes. In this talk I will focus on using gravitational waves from binary inspirals to probe the nature of compact objects and their interior composition. This is of particular interest for neutron stars which comprise matter at supra-nuclear density, under conditions not accessible anywhere else in the universe, whose detailed properties remain an important open question in subatomic physics. I will discuss the main gravitational-wave signatures of matter during a binary inspiral, methods for modeling these effects and extracting this information from the data, and what we have learned from the first observation of a neutron star binary inspiral GW170817. I will also highlight additional insights gained from joint electromagnetic counterpart information, and outline future prospects and challenges.

	Special Colloquium
Prof. Frank Bigiel	SCHEDULED

Argelander-Institut für Astronomie

This talk will provide an overview of some of the major research areas in our recently established group at the AIfA. While until the last few years extragalactic molecular gas surveys have been largely restricted to estimating masses and distributions often at low resolution based on one or very few CO lines, little information has been gained on the physical conditions of this gas across and among galaxies. With our IRAM EMPIRE survey and follow-up campaigns, probing a variety of different molecular lines at mm-wavelengths, as well as high-resolution, arcsecond-scale CO observations with ALMA, resolving molecular cloud scales across nearby galaxy samples, this is beginning to change. In combination with related efforts as part of our PHANGS collaboration, such as IFU imaging with VLT MUSE or HST observations, this is a powerful data set to derive a detailed inventory of gas physical conditions, star formation, stellar populations, and feedback across nearby galaxies. I will present these surveys, highlight results from EMPIRE and early results from PHANGS, and outline the prospects for the coming years. One of the key results of these efforts is a strong dependence of cold gas properties on host galaxy and dynamical environment within galaxies.