Press Releases Archive

31.01.2024

The X-ray sky opens to the world

First eROSITA sky-survey data release throws open largest ever catalogue of high-energy cosmic sources – University of Tübingen involved in consortium

Today, the German eROSITA consortium, in which the University of Tübingen’s Institute for Astronomy and Astrophysics (IAAT) is involved, 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) catalogue has yielded the largest X-ray catalogue ever published. Along with the data, the consortium released today a series of scientific papers describing new results ranging from studies of the habitability of planets to the discovery of the largest cosmic structures. Based on just the first six months of observations, eROSITA has already detected more sources than had previously been known in the 60-year history of X-ray astronomy. Now available to the worldwide science community, the data will revolutionise our knowledge of the Universe at high energies.

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 kilo-electronvolt, keV), the telescope detected 170 million X-ray photons, for which the cameras can accurately measure the incoming energy and arrival time. The catalogue was then constructed – after careful processing and calibration – by detecting concentrations of photons 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. That data will also be released to the world in the coming years.

The eRASS1 catalogue covers half the X-ray sky, the data share of 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 comprise more sources in 6 months than the big flagship missions XMM-Newton and Chandra have found in nearly 25 years of operation.

The IAAT is one of the five core institutes forming the German eROSITA consortium. “The results of the survey obtained by 250 scientists organized into 12 working groups and partially published alongside the data release, are of the highest quality and will help shed light on many aspects of X-ray astrophysics,” says Professor Andrea Santangelo, director of the IAAT. The High-Energy Astrophysics (HEA) group under his leadership contributed to the development of the mission, and, together with the Space-Based Astrophysics (SBA) Group led by Professor Beate Stelzer, participates in the national research network eRO-STEP (FOR2990) that is focused on the study of the endpoints of stellar evolution. This includes a wide range of objects – from white dwarfs with small companions (called Cataclysmic Variables) to Supernova Remnants.

“One puzzle about supernova remnants is their role in the acceleration of cosmic rays in our Milky Way,” says Dr. Gerd Pühlhofer from HEA group. “eROSITA significantly improves the ability to investigate several supernova remnants that are gamma-ray emitters, which identifies them as potential cosmic-ray accelerators. This is highly synergetic to the studies using other ground-based observatories in which our group is also involved.” Besides supernova remnants, the explosion of stars at the end of their lifetime leads to the formation of neutron stars, black holes, and white dwarfs. These different types of compact objects are key to our understanding of stellar evolution. “We try to find more of these extreme objects to better understand their origin and relation to normal stars. That’s a needle in a haystack problem – we only expect to find a few tens of neutron stars and black holes among millions of eROSITA sources, and have already found a few,” says Dr. Victor Doroshenko, eROSTEP co-investigator from the HEA group.

Professor Stelzer’s group also investigates X-ray emitting stars similar to our Sun and smaller objects called brown dwarfs. “eROSITA allows us for the first time in history to observe the variability of the stars’ X-ray light together with simultaneous data taken in visible light,” says Beate Stelzer. “We find extraordinary outbursts that are rare, and are identified only because with eROSITA we see so many stars.” Several of the new papers that appear today alongside with the data release, including the one that comprises the stellar flare from Fig.1, are led by doctoral students or young researchers from the University of Tübingen.

This first eRASS data release (DR1) makes public not only the source catalogue, but images of the X-ray sky at multiple X-ray energies and even lists of the individual photons with their sky positions, energies and precise arrival times. The software needed to analyse the eROSITA data is also included in the release. For many source classes, supplementary data from other wavebands has also been incorporated into value-added catalogues that go beyond pure X-ray information.

“The eROSITA collaboration makes an outstanding contribution to the international scientific community in terms of both publicly open data and scientific results,” adds Andrea Santangelo. “We are confident that the rest of the world will make the most of this enormous amount of observational data.”

Press release of the Max Planck Institute for Extraterrestrial Physics and the University of Tübingen

Fig.1 Superflare on a red dwarf star. The huge event was observed with eROSITA in X-ray light and simultaneously in optical light with the Transiting Exoplanet Survey Satellite (TESS) of NASA. The peak of the brightness in optical light precedes that of the X-ray light, and the decay phase lasts longer in X-rays. This time evolution is similar to observations of flares on our Sun. However, in the event shown here the red dwarf star has emitted in each of the two wavebands 100 000 more energy than what is produced by a solar flare.

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).

In these two images, a special image processing algorithm is used to separate extended features (left) from point sources (right).

Panning through the eROSITA sky

https://www.mpe.mpg.de/7989698/news20240131

In this animation, you can enjoy the X-ray sky as seen by eROSITA. The X-ray bands have been colour-coded according to their energy (red for 0.3-0.6 keV, green for 0.6-1 keV, blue for 1-2.3 keV) and a number of prominent sources have been highlighted.

Note to editors

eROSITA is the soft X-ray instrument aboard Spektrum-RG (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 German Space Agency at DLR (Deutsches Zentrum für Luft- und Raumfahrt). 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 telescope was launched into space onboard the SRG mission on July 13, 2019. Its large collecting area and wide field of view are designed to perform to a deep all-sky survey in the X-ray band. Over the course of six months (December 2019 to June 2020), SRG/eROSITA completed the first survey of the whole sky at energies 0.2-8 keV, which is significantly deeper than the only existing all-sky survey with an X-ray imaging telescope, performed by ROSAT in 1990 at energies 0.1-2.4 keV. Three more scans of the entire sky were completed between June 2020 and February 2022.

The German eROSITA Consortium is led by the Max Planck Institute for Extraterrestrial Physics (MPE), and includes the Dr. Karl Remeis Observatory Bamberg, the University of Hamburg Observatory, the Leibniz Institute for Astrophysics Potsdam (AIP), and the Institute for Astronomy and Astrophysics of the University of Tübingen, with the support of DLR and the Max Planck Society. The Argelander Institute for Astronomy of the University of Bonn and the Ludwig-Maximilians-Universität Munich also participate in the science exploitation of eROSITA as associated institutes. The eROSITA data are processed using the eSASS software system developed by the German eROSITA consortium.

eROSITA has been placed in Safe Mode in February 2022, and has not restarted science operations since.

Publications:

eRASS1 catalogue
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.

https://www.aanda.org/10.1051/0004-6361/202347165 m

Publications with first author from IAAT:
https://arxiv.org/abs/2401.17287
https://arxiv.org/abs/2401.17292
https://arxiv.org/abs/2401.17298
https://arxiv.org/abs/2401.17311
https://arxiv.org/abs/2401.17312

eRASS1 Facts & Figures:

Observation period: 12 December 2019 – 11 June 2020
Days of observations: 184
Observing efficiency (avg. fraction of time spent by the telescope collecting data): 96.5%
Total number of individual photons detected in the 0.2-2 keV energy range: 170 million [half-sky]
Total number of detected X-ray sources: ~900k [half-sky]
Total number of detected AGN (accreting supermassive black holes): ~710k [half-sky]
Total number of detected stars in the Milky Way: ~180k [half-sky]
Total number of detected clusters of galaxies: ~12k [half-sky]
Total volume of scientific data transmitted down to earth by the instrument: 75 GB [all-sky]
German eROSITA Consortium: ~250 members (incl. 80 early career researchers)

Contact:

Prof. Dr. Andrea Santangelo
University of Tübingen
Institut für Astronomie und Astrophysik (IAAT, Institute for Astronomy & Astrophysics)
Phone +49 7071 29-76128
santangelospam prevention@astro.uni-tuebingen.de

Prof. Dr. Beate Stelzer
University of Tübingen
Institut für Astronomie und Astrophysik (IAAT, Institute for Astronomy & Astrophysics)
Phone +49 7071 29-76132
stelzerspam prevention@astro.uni-tuebingen.de

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