Hunting for Dark Energy

Since the Big Bang, the Universe has been expanding. This expansion should actually be slowed down by the gravity of matter. But driven by Dark Energy, the expansion is accelerating. The physical phenomenon ‘Dark Energy’ is largely unexplained. The German X-ray telescope eROSITA (extended Roentgen Survey with an Imaging Telescope Array), which has been built under the auspices of the Max Planck Institute for Extra-terrestrial Physics in Garching, will shed light into the darkness. The project is supported by the DLR Space Administration with funds from the German Federal Ministry for Economic Affairs and Energy (BMWi).

Dark Energy is invisible and only noticeable on vast distances. How can it be investigated with an X-ray telescope? The key to this is galactic clusters – groups of up to several thousand individual galaxies. Their gravity attracts the surrounding hydrogen gas. This process is called accretion and produces very high temperatures which cause the gas to emit X-rays. Hence the clusters of galaxies become visible to eROSITA. eROSITA will study the distribution of approximately 100,000 galaxy clusters. By determining the distribution of galaxy clusters in space, astronomers can estimate the structure of the Universe today and in the past. This is possible since the light which arrives from large distances has been emitted a long time ago. Therefore, by mapping the distribution of galactic clusters, eROSITA will help to determine the nature of Dark Energy. This will be achieved by scanning the entire sky multiple times, observing many other phenomena and objects, such as active galactic nuclei, supernova remnants or X-ray binaries.

Far away from Earth, the seven-eyed telescope is the primary instrument of the Russian-German satellite mission ‘Spectrum-Roenten-Gamma’, which from 2019 will systematically scan the sky for X-ray sources. With special X-ray CCDs made of high-purity silicon cooled to minus 90 degrees Celsius and a mirror system composed of 378 galvanically replicated, thin-walled, gold-coated X-ray mirror shells, eROSITA optimally exploits the sparse incident X-ray light from the Universe and also permits detailed spectral analyses.

German Aerospace Center (DLR)
Thomas Mernik · E-Mail: ·


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