Active Galactic Nuclei (AGN) can form powerful collimated relativistic outflows, called jets, which carry a fraction of the total gravitational energy released during the accretion of matter onto a supermassive black hole (SMBH) at the centre of the AGN. Their jets emit brightly across the electromagnetic spectrum, often exhibit apparent superluminal motion, and are involved in the regulation of star formation and galaxy evolution via AGN feedback in the interstellar medium (ISM). Beyond the galaxy scale, AGN jets play a dominant role in heating the intracluster medium (ICM) and cause a substantial impact on the evolution of galaxy clusters and cosmological structure formation.
The formation of jets addresses long-standing fundamental physics questions related to the extraction of rotational energy from the central SMBH and the formation of
hydromagnetic flows from accretion disks around such compact objects. Imaging of AGN jets is now possible in the radio band using Very Long Baseline Interferometry (VLBI) at millimetre wavelengths, yielding unprecedented angular resolution of the jet-launching zone. It is now clear that AGN jets are emerging from SMBHs with foot points as small as a few gravitational radii, and very-high-energy gamma-ray observations have demonstrated the existence of emission regions even smaller than one gravitational radius. Recently, AGN jets have been associated with very-high energy neutrinos and are among the most likely candidates for the long sought-after sources of ultrahigh-energy cosmic rays.
These impressive observational breakthroughs within only a few years have moved AGN jets into the focus of modern astroparticle physics. However, fundamental questions regarding their composition, formation, collimation, and dissipation are still open:
1. How are relativistic jets launched from the vicinity of supermassive black holes? How are they accelerated and collimated?
2. Which radiative and dynamic processes govern the high-energy emission of AGN jets and what are AGN jets composed of?
3. How do AGN jets interact with their host galaxy? How does AGN feedback heat the ICM and which are the observational signatures?
This research unit brings together world-leading experts on theory, modeling, observation, and interpretation of all relevant angles of AGN-jet physics to deliver answers to these questions in the light of game-changing new observational information collected by the latest astronomical facilities at all observational wavelengths.
