The European Space Agency (ESA) has selected the Athena X-ray observatory for their next large (billion Euro-class) space mission.

One of the key science drivers of the Hot and Energetic Universe Science Theme is the study of the largest objects in the Universe, galaxy clusters, from ancient times, about ten billion years ago, when they first formed, down to the present. Most of the normal matter in these systems, intergalactic gas between the galaxies, is so hot, more than ten million degrees, that it is invisible in the optical but radiates at X-ray wavelengths. A team of astrophysicists from many institutes world-wide, including the Argelander Institute for Astronomy at Bonn University, demonstrated that the X-ray mission Athena has the technical capabilities to solve the outstanding questions about galaxy cluster evolution.

LINK: http://www.astro.uni-bonn.de/research/groups/dark-energy-group/projects-and-collaborations/athena/