eROSITA delivers the most comprehensive census of the high-energy Universe to date

The colour image shows X-ray sources in the western galactic hemisphere of the X-ray sky. The Galactic plane lies horizontally through the centre of the image. Sources in the eROSITA catalogue are plotted with their red, green and blue brightness showing their count rate in soft (0.5-1.0 keV), medium (0.5-1.0 keV) and hard (1.0-2.0 keV), respectively. The sky is plotted using an azimuthal equal area projection. © Jeremy Sanders / MPE

This figure compares the build-up of mass locked in super-massive black holes with the rescaled growth of the stellar population in inactive galaxies over cosmic time. The eROSITA X-ray census traces the fraction of super-massive black hole growth that is directly visible in the soft X-rays, while estimates including obscured sources show that much of the total growth is hidden from this view. The gap implies that roughly 70-90% of super-massive black holes' growth likely occurred in soft X-ray-suppressed phases. The shape similarity of all growth curves supports the claim that accreting super-massive black holes and galaxies evolved in lockstep, growing over broadly similar cosmic epochs. © William Roster / MPE

eROSITA DR2 Representation of the Active Galactic Nuclei (AGN)

This animation shows a representation of the active galactic nuclei (AGN) identified in the DR2 catalogue. Each dot shows a single object, where the distance from the three-dimensional centre increases with the source's redshift, i.e. how far away it is from us. We and our neighbouring objects lie at this centre. Sources at the same distance lie on shells, where the position of the dot on the shell is the position in the sky. The stationary circles, shown horizontally, represent the radii of the shells at redshifts of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5. The animation rotates about the western Galactic hemisphere, highlighting the clumpy nature of structure in the universe.

---

To the Point

• Catalogue contents, source types: DR2 lists over 1.9 million pointlike sources such as stars and supermassive black holes, plus about 64,000 extended sources including galaxy clusters and supernova remnants.


• Survey depth, sensitivity: Combining data from three fullsky scans, DR2 detects fainter X-ray fluxes and reveals many previously unknown sources.


• Multiwavelength identification: DR2 links X-ray detections to optical and infrared counterparts using six new catalogues, improving the understanding and classification of cosmic objects.


• Collaboration with SDSS: The release coincides with the Sloan Digital Sky Survey's twentieth data release, enabling 3D mapping of active black holes and studies on their growth across cosmic time.

---

Second data release nearly doubles the previously known eROSITA X-ray sources to two million

The German eROSITA Consortium (eROSITA-DE), led by the Max Planck Institute for Extraterrestrial Physics (MPE), has released its second major public dataset, eROSITA Data Release 2 (DR2). The new catalogue comprises close to two million X-ray sources—approximately doubling the number of previously released eROSITA sources in the X-ray sky and marking a major step forward in mapping the high-energy Universe. Built from the first three all-sky scans of the eROSITA telescope aboard the Spectrum-Roentgen-Gamma (SRG) mission, DR2 provides the most comprehensive catalogue of the X-ray Universe currently available to the scientific community. By combining multiple passes over the sky, the release significantly increases the survey depth and reveals large populations of previously undetected sources.

The main DR2 catalogue contains nearly two million X-ray sources detected in the 0.2–2.3 keV band and includes more than 1.9 million point-like sources, primarily stars and actively accreting supermassive black holes, as well as around 64,000 extended sources such as galaxy clusters, nearby galaxies, and supernova remnants. Compared to the first data release, the number of detected sources has roughly doubled.
v A complementary hard-band catalogue adds nearly 15,000 sources detected at higher energies (2.3–5.0 keV), tracing heavily obscured and intrinsically energetic systems that are often missed at softer X-ray energies. Together, these catalogues capture the full diversity of the X-ray sky, from nearby stellar coronae to distant supermassive black holes and massive galaxy clusters. Many of these objects are newly identified in X-rays, while others can now be studied with substantially improved precision.

After the start of operations in December 2019, eROSITA surveyed the entire sky every six months, progressively increasing depth and sensitivity. DR2 combines data collected over the mission’s first 556 days, spanning three full sky surveys (eRASS1–3). By stacking these observations, the survey reaches significantly fainter fluxes than the first release, enabling the large increase in detected sources.

“DR2 is the best inventory of the X-ray sky we have to date and opens the door to robust statistical studies of cosmic populations,” says Miriam E. Ramos-Ceja, Ground Segment Manager of the eROSITA instrument and lead author of the DR2 publication.

Linking X-rays to the broader Universe

To enable physical interpretation, DR2 includes multi-wavelength information that associates the X-ray detections with their most likely optical and infrared counterparts. Based on this information, roughly 88% are extragalactic, dominated by accreting supermassive black holes.

“X-ray detection is only the first step,” explains Mara Salvato, eROSITA spokesperson and chair of the follow-up working group. “By linking X-ray sources to their counterparts at other wavelengths, we can work out what these objects are, where they sit on the cosmic distance ladder, and build clean, well-defined samples on an unprecedented scale.”

A joint milestone with SDSS

The release coincides with the twentieth data release of the Sloan Digital Sky Survey (SDSS), which includes extensive optical spectroscopy of eROSITA-DE sources. Together, these datasets represent the culmination of nearly a decade of collaboration between the German eROSITA Consortium and the SDSS collaboration. By combining SDSS spectroscopy with eROSITA’s X-ray data, researchers can build three-dimensional maps of active black holes across the sky, revealing how these rapidly growing objects are distributed and evolve across cosmic time.

Combining eROSITA’s X-ray catalogue with spectroscopic and photometric redshifts enabled one of the largest and most detailed studies of accreting supermassive black holes to date. These elusive objects formed surprisingly early in the history of the Universe, and eROSITA has provided a new census of their growth at high redshift. “The most luminous black holes at high redshift are like needles in a haystack. Thanks to DR2 we found more needles than expected, suggesting that rapidly growing black holes were more abundant in the early Universe than previously thought” says William Roster, lead author of the corresponding study.

A focused, catalogue-driven release

In contrast to the first public data release, DR2 is a catalogue-focused release. It provides rigorously validated source lists derived from the combined eRASS:3 observations, along with an updated upper-flux-limit service that allows researchers to quantify non-detections across the sky.

The data cover the western Galactic hemisphere, reflecting the agreed data-sharing arrangement between the German and Russian eROSITA consortia. Within this region, DR2 represents the largest and most homogeneous public X-ray dataset currently available.

Enabling the next wave of discoveries

“This is a dataset of unprecedented scale and completeness, now in the hands of the global astronomical community,” says eROSITA Principal Investigator Andrea Merloni. “With nearly 2 million sources, DR2 provides a unique foundation for discoveries ranging from rare objects to large-scale population studies.” MPE Director Kirpal Nandra adds: “eROSITA just set another world record in terms of X-ray source numbers – and it won’t be the last.”

The eROSITA-DE DR2 catalogues, upper-flux-limit server, and full documentation are publicly accessible via the eROSITA-DE Science Data Archive.

Source: Max Planck Institute for Extraterrestrial Physics/Press Releases

---

Contacts:

Dr. Miriam Ramos-Ceja
Postdoc High-Energy Astrophysics
Tel: +49 89 30000-3603
Email: mramos@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics, Garching

William Roster
PhD-Student High-Energy Astrophysics
Tel: +49 89 30000-3879
Email: wroster@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics, Garching

Dr. Andrea Merloni
Senior Scientist High-Energy Astrophysics; PI eROSITA
Tel: +49 89 30000-3893
Email: am@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics

Dr. Mara Salvato
Senior Scientist High-Energy Astrophysics
Tel: +49 89 30000-3815
Email: mara@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics, Garching

Dr. Jeremy Sanders
Scientist High-Energy Astrophysics
Tel: +49 89 30000-3340
Email: jsanders@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics, Garching

Prof. Dr. Kirpal Nandra
Director of the High-Energy Astrophysics
Tel: +49 89 30000-3401
Email: knandra@mpe.mpg.de
Max-Planck-Institut für extraterrestrische Physik, Garching

---

Original publication

1. Ramos-Ceja, M.E., G. Lamer, M. Salvato, A. Merloni, J.S. Sanders et al. The SRG/eROSITA All-Sky Survey DR2: Cumulative X-ray catalogues from the first three surveys and multi-wavelength counterparts in the western Galactic hemisphere
A&A

Source | DOI

2. Roster, W., J. Buchner, M. Salvato, R. Shirley, A. Merloni et al.
Accrete, shine, repeat: AGN X-ray luminosity function
The SRG/eROSITA All-Sky Survey DR2
A & A

Source | DOI

---

Further Information

eROSITA website of the MPE

The X-ray sky opens to the world

With about 900 000 distinct sources, the first eROSITA All-Sky Survey (eRASS1) has yielded the largest X-ray catalogue ever published. 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.

eROSITA relaxes cosmological tension

February 14, 2024

Results from the first X-ray sky survey resolve the previous inconsistency between competing measurements of the structure of the Universe

Baryons at the Edge: SRG/eROSITA Survey Detects “Missing” Cosmic Gas at the Outskirts of Galaxy Clusters

May 05, 2026
Missing baryons found in galaxy cluster outskirts.
Research uncovers 90% of missing baryonic matter in galaxy cluster outskirts, enhancing cosmic structure understanding.

---

X-ray panorama of the “Manatee Nebula” by SRG/eROSITA

Figure 1 shows a composite X-ray image of the radio nebula W50 taken with the eROSITA telescope. The surface brightness of the X-ray emission is colour-coded in the 0.5–1 keV (red), 1–2 keV (green), and 2–4 keV (blue) energy bands. The white arrows depict the projection of the SS433 jets' precession cone extrapolated to distances of more than 100 pc. The hard and soft X-ray diffuse emission can be convincingly split into two components: softer filamentary emission (red-yellow) and harder (green-blue) emission from EXJs. Additionally, there are numerous nearby compact sources, such as active stars and accreting white dwarfs, as well as distant compact sources, mostly AGN. For distant sources, absorption by Milky Way gas suppresses emission below 1 or 2 keV, giving them a blue colour. © MPA; eROSITA/SRG

Figure 2 shows a schematic summary of the W50 nebula superimposed on a composite X-ray (red and green) and radio (VLA at 1.4 GHz, blue) image. Radio emission most likely arises at the outer, shell-like boundary of the nebula, while soft X-ray emission (0.3–0.9 keV) traces shock-heated interstellar medium (ISM) gas behind it, filling almost the entire interior of the nebula. The harder X-ray emission (0.9–2.7 keV in this case) is of a non-thermal (synchrotron) nature and may be produced by ultrarelativistic electrons that are accelerated at the shocks in the axial outflows from the system. The central part of the nebula, within 25 pc of SS433 (dashed circle), is likely to be of very low density and could be a wind-blown cavity created by an almost spherically symmetric outflow with a kinetic luminosity close to the Eddington limit. © MPA; eROSITA/SRG

---

Rare or unusual astrophysical objects are used to test the limits of theoretical models because of their extreme properties. The bright X-ray source SS433 in our galaxy undoubtedly belongs to this category. Initially identified as an Hα emitter, it was later recognised as a black hole in a binary system. Since then, SS433, which emits strongly in the radio and X-ray bands, has been targeted by almost every space- and ground-based observatory, leading to a flurry of discoveries.  In contrast, the surrounding huge W50 nebula, spanning more than two degrees, is much fainter and difficult to study. The complete radio image earned W50 the nickname 'Manatee Nebula', while X-ray maps were mostly patches from different observatories or lacked spatial or energy resolution. This shortcoming has finally been overcome by the recently published SRG/eROSITA map of W50 in multiple X-ray colours, which reveals a beautiful blend of thermal and non-thermal processes within an elongated cocoon.

At the core of the W50 nebula lies a compact source (most likely a stellar-mass black hole) that accretes matter from a companion star at an astonishingly high rate — thousands of times greater than the amount the black hole can digest. This limiting rate (known as the Eddington accretion rate) arises due to the pressure exerted by the radiation produced by the infalling gas. This configuration has an immediate impact on the observational appearance of the compact source and its large-scale environment. The key prediction of the accretion theory is that most of the gas supplied to the black hole will be expelled from the system, depositing a large amount of energy into the ambient medium in the process (see Highlight September 2024).

The W50 nebula is well known in radio astronomy for its croissant-like shape. Mapping this large nebula in X-rays used to be problematic due to the limited field of view of space telescopes. Additionally, strong and inhomogeneous absorption by gas and dust occurs in the direction of W50, which is located just two degrees away from the Galactic Plane. These problems can be resolved by using a telescope with a large field of view and high sensitivity to diffuse emission — the very characteristics of the eROSITA telescope on board the SRG observatory.

The full-size X-ray map of the W50 nebula is shown in Fig. 1. The central bright spot is the black hole that powers the entire nebula. It appears extended because it is much brighter than the nebula emission, causing the central part of the image to become saturated.

The 'X-ray colours' in this figure serve the same role as red, green, and blue colours in visible light. Specifically, red corresponds to X-ray photons with a longer wavelength, while green and blue correspond to progressively shorter wavelengths. Remarkably, this simple approach immediately reveals the nature of the X-ray emission: red and yellow colours dominate where thermal plasma with a temperature of 2–10 million degrees is present. Conversely, in the bluer regions, non-thermal emission from relativistic particles dominates.

The nebula is clearly asymmetric, most likely due to a gradient in the ambient gas density surrounding it. The most remarkable feature is the so-called 'Extended X-ray Jets' (EXJs), which have sharp inner edges located around 25 parsecs from the central black hole SS433. Their spectra do not have the emission lines characteristic of thermal plasma. Rather, they must be due to the emission of relativistic particles accelerated by shocks powered by SS433’s outflows. These structures have recently been detected at TeV energies; each TeV photon carries a billion times more energy than a soft X-ray photon at keV energies.

These new X-ray data support the idea that the energy flow from SS433 evolves through three distinct stages:

1) an invisible 'dark' flow of energy between the black hole and the EXJs, presumably carried by a cold wind from the binary system;

2) a 'non-thermal' flow of energy over some 30 pc in the form of EXJs; and

3) a thermal flow (i.e., shock-heated interstellar medium (ISM)) that envelops the EXJs.

The thermal part of the W50 X-ray emission can be reasonably well described by a shock-heated plasma that has not yet reached temperature and ionisation equilibrium. Such emission is typical of middle-aged or old supernova remnants (SNRs). The outer radio boundary of the nebula also resembles SNR shocks (see Fig. 2).

In contrast, the 'extended X-ray jets' are the most remarkable features of this system on tens-of-pc scales. Their sharp inner edges plausibly correspond to extreme shocks that accelerate particles and power the X-ray (synchrotron) and TeV emission, which is 9–10 orders of magnitude more energetic. The W50/SS433 system clearly illustrates the important role that hyper-Eddington accretors might play in the energetics of the interstellar medium in galaxies at different redshifts, as well as in the production of ultra-high-energy particles.

Source: Max Planck Institute for Astrophysics/Research Highlights

---

Authors:

Rashid Sunyaev
Emeritus Director
Tel: 2244
Email: rsunyaev@mpa-garching.mpg.de

Eugene Churazov
Scientific Staff
Tel: 2219
Email: echurazov@mpa-garching.mpg.de

---

Original publication

Sunyaev R., Khabibullin I., Churazov E., Gilfanov M., Medvedev P., Sazonov S.
X-ray panorama of the SS433/W50 complex by SRG/eROSITA
A&A, in press

DOI

---

One sixth of the sky with the telescope SRG/eROSITA

Current status of the all-sky survey in X-rays by SRG: about 1/6 of the entire sky has already been covered. Due to the survey geometry, the individual scans of the observatory intersect near the ecliptic poles, resulting in increased sensitivity. The inset shows a small region enlarged and a PLANCK map of the same region in comparison. © IKI, MPA

A little more than a month has passed since the beginning of the regular all-sky survey of the SRG observatory, moving on a halo orbit around the Sun-Earth Lagrange point L2. The spacecraft is at a distance of one and a half million kilometers from Earth, rotating around an axis directed towards the Sun. Since the start of the scan, the ART-XC and eROSITA telescopes have already covered more than 1/6 of the entire celestial sphere and demonstrated the excellent capabilities of SRG in mapping the X-ray sky. By mid-June 2020, the scientists will have the first map of the entire sky, and after four years, each part of the sky will be covered 8 times, increasing the sensitivity of the survey by a record 20-30 times compared to the existing one by the ROSAT satellite.

The image shows a map of half the sky in the 0.4–2 keV energy range, obtained by the SRG/eROSITA telescope. The axes of the observatory telescopes draw large circles in the sky passing through the north and south ecliptic poles. The dark band associated with the absorption of soft X-ray radiation by gas and dust in the Galaxy Plane is clearly visible on the map. The bright diffuse region on the right side of the map is the famous North Polar Spur, an area of ​​increased brightness of radio emission in the form of an arc. Another bright area near the Plane of the Galaxy is the most powerful star-forming region in our Galaxy, known as Cygnus X. Outside of these areas, the X-ray radiation is dominated by numerous active galactic nuclei and clusters of galaxies.

The resolution of the map of the whole sky shown in the figure does not allow one to see individual sources, although more than ten thousand of them have already been registered. To illustrate the capabilities of the telescope, the inset shows a small portion of the sky (2x2 degrees) with better resolution. For comparison the PLANCK (ESA) SZ-map of the same region is shown. The place where the inset was taken from is shown in the large image as a small square near the North ecliptic pole. Near the ecliptic poles the individual scans of the observatory intersect.

The Spectrum RG Observatory continues to scan, and every day it adds a 1-degree-wide strip to this map. The images shown here are based on the data from the Russian share of observing time of the SRG/eROSITA telescope.

Contacts

Rashid Sunyaev
Director emeritus
Tel: 2244
rsunyaev@mpa-garching.mpg.de

Eugene Churazov
Scientific Staff
Tel: 2219
echurazov@mpa-garching.mpg.de

Marat Gilfanov
Scientific Staff
Tel: 2227
mgilfanov@mpa-garching.mpg.de

Source: Max Planck Institute for Astrophysics/News

---