The AGN phenomenon: open issues

TL;DR

This paper highlights key unresolved questions about Active Galactic Nuclei (AGN), emphasizing the need for advanced observations and models to understand their central engines, jet formation, and emission mechanisms.

Contribution

It summarizes the main open issues in AGN research and proposes future research directions and tools to address these fundamental questions.

Findings

Identification of key open questions in AGN physics

Proposed research strategies including surveys and simulations

Emphasis on bridging observational gaps in the MeV range

Abstract

The aim of this short paper is to motivate and encourage research in the field of Active Galactic Nuclei (AGN). Here we summarize the main open questions concerning the central engine. Is the central black hole rapidly spinning and can we prove this? What is the dominant accretion mechanism in AGN? Why do some AGN form jets while others don't and how do the jets originate? What keeps jets collimated out to distances of 100 kpc? Is the emission of blazars dominated rather by synchrotron self-Compton or by external Compton processes? Which parameters are important in the unified model? We outline the status of related research, formulate the questions and try to hint at research projects able to tackle these fundamental topics. Deep surveys, polarization measurements, improved models, faster and more accurate simulations as well as bridging the gap in the MeV range can be part of the tools to bring us closer to an understanding of AGN.