Athena (the Advanced Telescope for High-Energy Astrophysics), has been proposed as ESA's next-generation X-ray astronomy observatory. It has been conceived to address two key questions in modern astrophysics:
- How does ordinary matter form the large-scale structures that we see today?
- How do black holes grow and shape the Universe?
Athena will provide a huge leap in observational capabilities compared to current X-ray astronomy facilities, providing factor ~10 improvements in imaging high-resolution spectroscopy and wide field X-ray imaging. These advances are need to determine the astrophyiscal processes responsible for the evolution of the hot gas over cosmic time, the end point of which are clusters, groups and filaments which dominate the baryonic content of the Universe. Feedback from supermassive black holes apparently plays a major role in determining the evolution of these large baryonic structures, as well as that of galaxies. Athena will also perform a census of black hole activity stretching out to the highest redshifts (z>6) and identifying even the most obscured systems shrouded in dust and gas, possibly due to the feedback process itself. Spectroscopy and timing studies of nearby accreting black holes will shed light on the processes causing feedback - which ultimately originate close to the black hole event horizon - and the mechanisms by which the radiative and/or mechanical output of the black hole couples to larges scales, where it has such an apparently profound effect.