The German eROSITA Consortium (eROSITA-DE), led by the Max Planck Institute for Extraterrestrial Physics (MPE), released eROSITA Data Release 2 (DR2), assembling nearly two million X-ray sources to build the most comprehensive census of the high-energy universe to date, according to a statement from MPE and the corresponding study led by researchers like William Roster and Miriam E. Ramos-Ceja.
Inside the eROSITA DR2 High-Energy Universe Catalog
The new catalog nearly doubles the previously known eROSITA X-ray sources, reaching close to two million detections in the 0.2–2.3 keV band. According to the German eROSITA Consortium, the dataset combines observations obtained over the Spectrum-Roentgen-Gamma (SRG) mission’s first 556 days. The observatory scanned the entire sky every six months starting in December 2019, completing three full sky surveys (eRASS1–3).
By stacking these observations, the survey reached significantly fainter fluxes than the first release. According to project scientists, the main catalog includes over 1.9 million point-like sources, primarily stars and actively accreting supermassive black holes, alongside roughly 64,000 extended sources such as galaxy clusters, nearby galaxies, and supernova remnants.
Did you know? DR2 also features a complementary hard-band catalog containing nearly 15,000 sources detected at higher energies between 2.3 and 5.0 keV. According to the research team, this higher-energy sweep captures heavily obscured and intrinsically energetic systems that softer X-ray scans usually miss.
Multi-Wavelength Identification and SDSS Collaboration
Detecting X-rays marks only the initial phase of mapping the high-energy sky. According to Mara Salvato, eROSITA spokesperson and chair of the follow-up working group, researchers linked X-ray detections to optical and infrared counterparts using six new catalogs. This multi-wavelength approach helps astronomers determine object types, establish their position on the cosmic distance ladder, and build well-defined samples on an unprecedented scale.
This release aligns with the Sloan Digital Sky Survey’s twentieth data release (SDSS DR20). Combining eROSITA-DE survey data with SDSS optical spectroscopy represents nearly a decade of scientific collaboration. According to the research team, this joint effort enables massive 3D mapping of active black holes to track their evolution across cosmic time.
Early Black Holes and Accreting Supermassive Systems
Data from the survey indicates that roughly 88% of the identified sources are extragalactic, originating predominantly from actively accreting supermassive black holes at the centers of distant galaxies. William Roster, lead author of a corresponding study, noted that luminous black holes at high redshift resemble needles in a haystack. Thanks to DR2, researchers located more of these objects than expected, implying that rapidly growing black holes were far more abundant in the early Universe than previous models suggested.
“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,” said Miriam E. Ramos-Ceja, Ground Segment Manager of the eROSITA instrument and lead author of the DR2 publication, via an MPE statement.
Frequently Asked Questions
What is eROSITA Data Release 2 (DR2)?
eROSITA DR2 is the second major public dataset from the German eROSITA Consortium, providing an inventory of nearly two million X-ray sources across the high-energy sky.
How many sources are included in the new catalog?
The release features nearly two million X-ray sources in its main catalog—roughly doubling the count from the first data release—alongside roughly 15,000 hard-band sources and 64,000 extended sources.
What instrument captured the data?
The data was gathered by the eROSITA telescope, the primary instrument aboard the Russian-German Spektr-RG (SRG) space observatory.
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