The X-ray sky opens to the world

Today, the German eROSITA consortium released the data for its share of the first all-sky survey by the soft X-ray imaging telescope flying aboard the Spectrum-RG (SRG) satellite. With about 900,000 distinct sources, the first eROSITA All-Sky Survey (eRASS1) has published the most extensive X-ray catalogue. Based on just the first six months of observations, eROSITA has already detected more sources than previously known in the 60-year history of X-ray astronomy.

This image show half of the X-ray sky, projected onto a circle (so-called Zenit Equal Area projection) with the centre of the Milky Way on the left and the galactic plane 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). Image: MPE, J. Sanders for the eROSITA consortium

The eRASS1 observations with the eROSITA telescope were carried out from 12 December 2019 to 11 June 2020. In the most sensitive energy range of the eROSITA detectors (0.2-2 keV), the telescope detected 170 million X-ray photons, for which the cameras can accurately measure the incoming energy and arrival time. After careful processing and calibration, the catalogue was then constructed by detecting photon concentrations in the sky against a bright, large-scale, diffuse background. After eRASS1, eROSITA has continued scanning the sky and accumulated several additional all-sky surveys. Those data will also be released to the world in the coming years.
The eRASS1 catalogue covers half the X-ray sky, the data shared by the German eROSITA consortium. It consists of more than 900 000 sources, including some 710 000 supermassive black holes in distant galaxies (active galactic nuclei), 180 000 X-ray emitting stars in our own Milky Way, 12 000 clusters of galaxies, plus a small number of other exotic classes of sources like X-ray emitting binary stars, supernova remnants, pulsars, and other objects. “These are mind-blowing numbers for X-ray astronomy,” says ORIGINS scientist Andrea Merloni. He is the principal investigator of eROSITA and the first author of the eROSITA catalogue paper. “We’ve detected more sources in 6 months than the big flagship missions XMM-Newton and Chandra have done in nearly 25 years of operation.”

Scientific publications on the habitability of planets up to the discovery of the largest cosmic structures

Coordinated with the release, the German eROSITA Consortium has submitted almost 50 new scientific publications to peer-reviewed journals, adding to the more than 200 that the team had already published before the data release. Most of the latest papers appear today (see link below) with selected discoveries, including a giant filament of pristine warm-hot gas extending between two galaxies and two new 'Quasi-Periodically Erupting' black holes. Further, the papers contain studies of how X-ray irradiation from a star may affect orbiting planets' atmosphere and water retention and statistical analysis of flickering supermassive black holes.

"The scientific breadth and impact of the survey is quite overwhelming; it's hard to put into a few words," says ORIGINS scientist Mara Salvato, who, as spokesperson for the German eROSITA consortium, coordinates the efforts of about 250 scientists organised into 12 working groups. "But the papers published by the team will speak for themselves."


Publication: Merloni et al.: The SRG/eROSITA all-sky survey, First X-ray catalogues and data release of the Western Galactic hemisphere, A&A volume 682, A34

Press Release of the Max Planck Institute for extraterrestrial physics (MPE)


Dr. Andrea Merloni
Max Planck Institute for extraterrestrial physics / Excellence Cluster ORIGINS
email: am(at)

Dr. Mara Salvato
Max Planck Institute for extraterrestrial physics / Excellence Cluster ORIGINS
email: mara(at)