The German Aerospace Center (DLR) and Russia’s Roskosmos space agency are joining forces to try and shed some light on the poorly understood phenomenon referred to as ‘dark energy’. In 2012 the German extended Roentgen Survey with an Imaging Telescope Array (eROSITA) X-ray telescope will be taken into orbit on board the Russian Spektrum Roentgen Gamma (SRG) satellite to start searching for black holes and dark matter in an attempt to answer why the expansion of the universe is accelerating instead of slowing down.

Consisting of seven individual mirror systems with apertures of just under 36 centimeters and 54 nested mirror shells each, which scan the whole sky in parallel, the eROSITA telescope will offer an unparalleled combination of collecting area, field-of-view and resolution. Acting as seven electronic eyes are specially developed CCDs (Charge Coupled Devices) placed at the focal point of each X-ray mirror system.

To investigate dark energy, which is invisible and 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 that has collected at their centers. It is the distribution of this gas in space and its variation over time that is the key to the analysis of the characteristics of dark energy. Clues may be found, for example, in 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.

Unlike radio astronomy, which studies the radio waves from an astronomical object, X-ray astronomy is an observational branch of astronomy that deals with the study of X-ray emissions from celestial objects. And since X-ray radiation is absorbed by the Earth’s atmosphere, X-ray telescopes such as eROSITA must be sent into space.

The eROSITA will be carried into space on a Soyuz-Fregat rocket that will set the X-ray telescope into an orbit around the second Lagrange (L2) point of the Sun-Earth system. L2 is one of five positions in an orbital configuration that a small object affected only by gravity will be stationary relative to the two larger objects, in this case the Sun and the Earth. L2 is located approximately 1.5 million kilometers behind Earth as seen from the Sun and is particularly good as a site for performing astrophysical observations. From this position, eROSITA will observe the whole sky for seven years and scan it multiple times.

Members of the German Aerospace Center and Roskosmos recently signed a detailed agreement setting out all the organizational and technical boundary conditions for the eROSITA project, which should provide scientists with valuable new findings to hopefully answer some of the big questions about our universe: How was it created? How old is it? What is its future?

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