31. January 2024

eROSITA: The X-ray sky opens to the world eROSITA: The X-ray sky opens to the world

Consortium including University of Bonn researchers makes public the largest ever catalogue of high-energy cosmic sources

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) catalogue has yielded the largest X-ray catalogue ever published. Along with the data, the consortium released today more than 40 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 revolutionize our knowledge of the high-energy Universe.

Download all images in original size (c) Jakob Dietl, Argelander-Institut für Astronomie / Universität Bonn

The eROSITA space telescope entered outer space on July 13, 2019 from Baikonur attached to a Proton-M launch vehicle. Because high-energy X-rays are fully absorbed by the Earth’s atmosphere, this is the only way to carry out these observations. The data that has now been published represents the first of many all-sky surveys using the eROSITA telescope. Within the most sensitive energy range of the eROSITA detectors, the telescope detected 170 million X-ray photons during this time, whose incoming energy and arrival time can be measured precisely using the cameras.

The eRASS1 catalogue covers half the X-ray sky and represents the data share attributable to 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 and 12,000 clusters of galaxies, plus a small number of other exotic classes of sources such as X-ray-emitting binary stars, supernova remnants, pulsars, and other objects.

“These are mind-blowing numbers for X-ray astronomy,” says Andrea Merloni, eROSITA principal investigator and 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.”

To coincide with the release, the German eROSITA Consortium has submitted more than 40 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 new papers appear today with selected discoveries including the giant filament of pristine warm-hot gas extending between two galaxy clusters. Further studies of how X-ray irradiation from a star may affect the atmosphere and water retention of orbiting planets.

“The scientific breadth and impact of the survey is quite overwhelming; it’s hard to put into a few words,” says Mara Salvato, who as spokesperson for the German eROSITA consortium co-ordinates the efforts of about 250 scientists organized into 12 working groups. “But the papers published by the team will speak for themselves.”

The first authors also include astrophysicists from the University of Bonn led by Prof. Dr. Thomas Reiprich from the Argelander Institute for Astronomy. “The hot gas inside clusters of galaxies (>10 million degrees Celsius) can be observed especially well within the X-ray range,” says Jakob Dietl, a master’s student at the Argelander Institute. “According to our theoretical models of the cosmos, these clusters should be connected by filaments of hot gas (1–10 million degrees Celsius). eROSITA has now enabled us to discover and describe a particularly long filament between two clusters for the first time.” But eROSITA is also ideal for investigating the clusters themselves: “The instrument’s large field of view has allowed us to study not only details of our nearest cluster, the Virgo Cluster, but also the area around it,” explains Hannah McCall, who is now studying for a doctorate at the University of Chicago having completed her master’s thesis at the University of Bonn. She adds: “If we could see Virgo in the night sky with the naked eye, it’d have a diameter equivalent to 15 full moons, so eROSITA is just made for analyzing objects like these. It’s the first time we’ve been able to study the outer regions of the Virgo Cluster on a grand scale.” Another researcher, Dr. Konstantinos Migkas, who obtained his doctorate from the University of Bonn and is now Oort Postdoctoral Fellow at Leiden Observatory, carried out important cross-calibration work with other X-ray satellites and is first author of a further study.

One of the research aims being pursued by the telescope is to use clusters of galaxies to test cosmological models. The cosmological findings based on a detailed analysis of the eRASS1 clusters will be published in around two weeks.

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)

Animation regarding the filament between galaxy clusters: https://www.youtube.com/watch?v=Uqye0DfOWII

Animation of Virgo: https://youtu.be/KsdDmsG_uTQ

eROSITA X-ray image with the newly discovered filament between two galaxy clusters.
eROSITA X-ray image with the newly discovered filament between two galaxy clusters. - The distribution of galaxies (white contours), as seen from the Two Micron All Sky Survey, follows the structure of the filament. In the SLOW simulation, which is tailored to reproduce the main features of the Local Universe, this individual system with both clusters and the filament spine is reproduced as well. © Dietl et al. (2024), University of Bonn
This X-ray image shows the full extent of the Virgo Cluster,
This X-ray image shows the full extent of the Virgo Cluster, - which is the closest galaxy cluster (collection of galaxies) to us. The bright white spot at the center is the central galaxy M87 (known for the picture of the supermassive blackhole as observed by the Event Horizon Telescope). The hazy white glow around M87 is the very hot gas between galaxies. It extends out more in some directions than others, and isn’t circular; this is evidence that the Virgo Cluster is still in the process of forming. The colourful stripe in the bottom left comes from foreground emission inside our own galaxy and is known as one of the eROSITA bubbles. © McCall et al. (2024), University of Bonn

eROSITA is the soft X-ray instrument aboard Spectrum-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.

Jakob Dietl
Argelander-Institut für Astronomie, Universität Bonn
E-Mail: jdietl@astro.uni-bonn.de

Hannah McCall
Department of Astronomy and Astrophysics, University of Chicago
E-Mail: hannahmccall@uchicago.edu

Prof. Dr. Thomas Reiprich
Argelander-Institut für Astronomie, University of Bonn
Phone: +49 228 73 3642
E-Mail: reiprich@astro.uni-bonn.de

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