The German eROSITA (extended ROentgen Survey with an Imaging Telescope Array) X-ray telescope is to start searching for black holes and dark matter in 2012, using seven electronic 'eyes'.

On 18 August 2009, executive board members of the German Aerospace Center and the Russian space agency Roskosmos signed a detailed agreement during the MAKS International Aviation and Space Salon in Moscow, setting out all the organisational and technical boundary conditions for the eROSITA project.

As long ago as March 2007, a memorandum of understanding defined the willingness of the agencies to collaborate in principle on this project.

"This scientifically highly-demanding project is a beacon project of scientific collaboration in space between Russia and Germany," DLR executive board chairman Prof. Johann-Dietrich Worner said. Prof. Worner continued: "It is my understanding that with this collaboration we can draw on the experience of the past not just with regard to unmanned space flight."

eROSITA will be taken into orbit in 2012 from the Russian Baikonur cosmodrome on board the Russian Spektrum Roentgen Gamma (SRG) satellite. A Soyuz-Fregat rocket will take the satellite into an orbit around the second Lagrange point of the Sun-Earth system, L2.

This point, located approximately 1.5 million kilometres behind Earth as seen from the Sun, is particularly good as a site for performing astrophysical observations. The European Herschel and Planck space telescopes have been in orbit around L2 since July 2009. From this position, eROSITA will observe the whole sky for seven years and scan it multiple times.

eROSITA: on the track of dark matter
The universe has been expanding ever since the Big Bang - and this expansion might be expected to be slowing down under the influence of gravity. Instead, the expansion is accelerating, driven by a poorly understood phenomenon referred to as 'dark energy'. eROSITA is intended to shed light on the darkness. The X-ray telescope is being built under the lead management of the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, near Munich.

"The internationally strong position in X-ray astronomy that we have acquired in Germany through our participation in missions such as Rosat, XMM-Newton (X ray Multi-Mirror) and Chandra (Chandra X-Ray Observatory) will continue to grow," Gerold Reichle, a DLR executive board member, said.

"The results of the eROSITA mission will provide the international community of scientists with valuable new findings for a deeper understanding of the processes in the universe," Reichle continued.

German eROSITA telescope to be a new star in the sky
Construction of the new eROSITA telescope began in 2007, since the production of the mirrors and the cameras takes a long time. "Forty-five scientists, engineers and technicians are employed on its development and construction at the MPE alone," said Dr. Peter Predehl, the project's lead scientist from the Max Planck Institute for Extraterrestrial Physics, adding: "eROSITA is a world-leading instrument for X-ray astronomy, both scientifically and technologically."

The German X-ray telescope consists of seven individual mirror systems with apertures of just under 36 centimetres for radiation ingress and 54 nested mirror shells each, which will scan the whole of the sky in parallel. The combination of collecting area, field-of-view and resolution is unparalleled.

At the focal point of each X-ray mirror system, there is a CCD (Charge Coupled Device) camera specially developed for eROSITA. The seven electronic 'eyes' must be cooled to a temperature of below 80 degrees Celsius during operation.

The cameras utilise expertise from the semiconductor laboratory maintained by the Max Planck Institutes for Physics and for Extraterrestrial Physics in Garching, which is the source for the most sensitive X-ray detectors in the world - used, for example, in the European XMM-Newton and Rosetta space probes as well as the two US Mars rovers Spirit and Opportunity.

X-ray astronomy - science par excellence
How is the eROSITA x-ray telescope going to be used to investigate dark energy, which is invisible and is only perceptible at vast distances?

eROSITA will survey about 100 000 galaxy clusters, which are visible to the X-ray telescope through the radiation from the hot gas which has collected at their centres. Their distribution in space and its variation over time - we are, after all, looking at these objects in the past because of the finite speed of light - are the key to the analysis.

Characteristics of dark energy can be derived, for example, from the way that its share in the energy density of the universe, which it dominates today at more than 70 percent, has changed in the course of cosmic evolution. Ultimately, these investigations lead to basic questions about our universe: How was it created? How old is it? What is its future?

Many different institutions and companies are contributing to finding the answers to such questions: the Max Planck Institutes for Extraterrestrial Physics and for Astrophysics, both in Garching near Munich, the Institute of Astronomy and Astrophysics of the University of Tubingen, the Potsdam Astrophysics Institute, the Hamburg University Observatory, the Dr Remeis Observatory in Bamberg, the German Aerospace Center, Roskosmos and the Space Research Institute in Moscow, Kayser-Threde GmbH, Carl Zeiss AG and Medialario Technologies (Italy).