The energetic universe as seen with the eROSITA X-ray telescope. The first eROSITA all-sky survey was conducted over a period of six months by letting the telescope rotate continuously, thus providing a uniform exposure of about 150-200 seconds over most of the sky, with the ecliptic poles being visited more deeply. As eROSITA scans the sky, the energy of the collected photons is measured with an accuracy ranging from 2% – 6%. To generate this image, in which the whole sky is projected onto an ellipse (so-called Aitoff projection) with the centre of the Milky Way in the middle and the body of the Galaxy running horizontally, photons have been colour-coded according to their energy (red for energies 0.3-0.6 keV, green for 0.6-1 keV, blue for 1-2.3 keV). The original image, with a resolution of about 10”, and a corresponding dynamic range of more than one billion, is then smoothed (with a 10’ FWHM Gaussian) in order to generate the above picture.The red diffuse glow away from the galactic plane is the emission of the hot gas in the vicinity of the solar system (the Local Bubble). Along the plane itself, dust and gas absorb the lowest energy X-ray photons, so that only high-energy emitting sources can be seen, and their colour appears blue in the image. The hotter gas close to the galactic centre, shown in green and yellow, carries imprinted the history of the most energetic processes in the life of the Milky Way, such as supernova explosions, driving fountains of gas out of the plane, and, possibly, past outburst from the now dormant supermassive black hole in the centre of the galaxy. Piercing through this turbulent, hot diffuse medium, are hundreds of thousands of X-ray sources, which appear mostly white in the image, and uniformly distributed over the sky. Among them, distant active galactic nuclei (including a few emitting at a time when the Universe was less than one tenth of its current age) are visible as point sources, while clusters of galaxies reveal themselves as extended X-ray nebulosities. In total, about one million X-ray sources have been detected in the eROSITA all-sky image, a treasure trove that will keep the teams busy for the coming years.

Photo credit: Jeremy Sanders, Hermann Brunner and the eSASS team (MPE); Eugene Churazov, Marat Gilfanov (on behalf of IKI)

Date: 19 June 2020

Institution: Max Planck Institute for Extraterrestrial Physics (MPE)

Digest: eROSITA X-ray telescope onboard on Russian-German SRG (“Spectrum-Roentgen-Gamma”) has completed its first full sweep of the sky in 182 days. Researchers had generated a new map of the hot, energetic universe. Clusters of galaxies in the new map will be used to track the growth of cosmic structures and constrain cosmological parameters.

Over the course of 182 days, the eROSITA X-ray telescope onboard SRG has completed its first full sweep of the sky. This new map of the hot, energetic universe contains more than one million objects, roughly doubling the number of known X-ray sources discovered over the 60-year history of X-ray astronomy. “This all-sky image completely changes the way we look at the energetic universe,” says Peter Predehl, the Principal Investigator of eROSITA at the Max Planck Institute for Extraterrestrial Physics (MPE). “We see such a wealth of detail – the beauty of the images is really stunning.”

Assembling the image has been a mammoth task. This first complete sky image from eROSITA is about 4 times deeper than the previous all-sky survey by the ROSAT telescope 30 years ago. Most of the new sources are active galactic nuclei at cosmological distances, marking the growth of gigantic black holes over cosmic time. Clusters of galaxies in the new map will be used to track the growth of cosmic structures and constrain cosmological parameters. Closer to home, stars with hot coronae, binaries and supernova remnants dot our Galaxy, and we now have a complete map of the hot baryons in the Milky Way, something that can only be achieved with the 360-degree view provided by the eROSITA survey.

The “Vela supernova remnant“ which is shown here is one of the most prominent objects in the X-ray sky. The bright blue point source in the middle of the image is the Vela pulsar. Photo: Peter Predehl, Werner Becker (MPE), Davide Mella

Research groups in the LMU Faculty of Physics have been involved in the preparation for eROSITA since 2009. The Cosmology and Structure Formation research group, led by Joseph Mohr, is responsible for the cross-identification of the X-ray identified galaxy clusters from the eROSITA sky survey with their optical galaxy counterparts, providing redshifts or distances to each of the thousands of newly discovered systems. The preparatory work has enabled the construction of the new galaxy cluster catalogs including redshifts in record time, with Matthias Klein providing the first version of the cluster catalog to the eROSITA collaboration within a week from the end of the survey. Other Cosmology and Structure Formation group members are focused on using gravitational lensing to measure the cluster masses and in contributing their expertise to the cosmological and astrophysical study of these systems.

The Physical Cosmology research group, led by Jochen Weller, plans to use the new cluster catalog to identify a new catalog of voids– large empty regions of low density that mark the large scale structure of our Universe. Members of Andreas Burkert‘s Computational Astrophysics Group, including Klaus Dolag, focus on using their hydrodyanical simulations of structure formation to enable precise studies of the physical processes responsible for the formation and evolution of both the active galactic nuclei and the galaxy clusters. These LMU research groups all work in close collaboration with the rest of the eROSITA science team, located at MPE and the other eROSITA institutions within Germany.

On 11 June 2020, the eROSITA telescope completed its first survey of the entire X-ray sky. Launched on 13 July 2019 on-board the SRG spacecraft and now orbiting the second Lagrange point of the Earth-Sun-system, the telescope is in continuous scanning mode. During the first all-sky survey, each point in the sky was exposed to the eROSITA telescope for an average duration of 150-200 seconds. The regions close to the ecliptic poles, where the great circles traced by the telescope on the sky intersect, were revisited many times, accumulating exposures of up to a few hours. SRG will continue scanning the sky for three and half years more, with eROSITA performing seven more all-sky surveys in the process.

eROSITA is the primary instrument aboard SRG, a joint Russian-German science mission supported by the Russian Space Agency (Roskosmos), in the interests of the Russian Academy of Sciences represented by its Space Research Institute (IKI), and the Deutsches Zentrum für Luft- und Raumfahrt (DLR). The SRG spacecraft was built by Lavochkin Association (NPOL) and its subcontractors, and is operated by NPOL with support from the Max-Planck Institute for Extraterrestrial Physics (MPE).

The eROSITA data shown here were processed using the eSASS software system developed by the German eROSITA consortium.

Source: Max-Planck Institute for Extraterrestrial Physics (MPE)