The deepest view of the X-ray sky

The eROSITA telescope has provided a new, sharp view of hot and energetic processes across the Universe.

The eROSITA X-ray telescope has completed its first full sweep of the sky. This new map of the hot, energetic universe contains more than one million objects, roughly doubling the number of known X-ray sources discovered over the 60-year history of X-ray astronomy. Most of the new sources are active galactic nuclei at cosmological distances, marking the growth of gigantic black holes over cosmic time. Clusters of galaxies in the new map will be used to track the growth of cosmic structures and constrain cosmological parameters. Closer to home, stars with hot coronae, binaries and supernova remnants dot our Galaxy, and we now have a complete map of the hot baryons in the Milky Way.

“This all-sky image completely changes the way we look at the energetic universe,” says Peter Predehl, the Principal Investigator of eROSITA at the Max Planck Institute for Extraterrestrial Physics (MPE). “We see such a wealth of detail – the beauty of the images is really stunning.”

This first complete sky image from eROSITA is about 4 times deeper than the previous all-sky survey by the ROSAT telescope 30 years ago. “We were all eagerly awaiting the first all-sky map from eROSITA,” says Mara Salvato, the scientist at MPE who leads the effort to combine eROSITA observations with other telescopes across the electromagnetic spectrum. “Large sky areas have already been covered at many other wavelengths, and now we have the X-ray data to match.”

While the team is now busy analysing this first all-sky map and using the images and catalogues to deepen our understanding of cosmology and high-energy astrophysical processes, the telescope continues its sweep of the X-ray sky. “The SRG Observatory is now starting its second all-sky survey, which will be completed by the end of this year“, says Rashid Sunyaev, Lead Scientist of the Russian SRG team. “Overall, during the next 3.5 years, we plan to get 7 maps similar to the one seen in this beautiful image. Their combined sensitivity will be a factor of 5 better and will be used by astrophysicists and cosmologists for decades.“

Kirpal Nandra, head of the high-energy astrophysics group at MPE, adds “With a million sources in just six months, eROSITA has already revolutionized X-ray astronomy, but this is just a taste of what’s to come. This combination of sky area and depth is transformational. We are already sampling a cosmological volume of the hot Universe much larger than has been possible before. Over the next few years, we’ll be able to probe even further, out to where the first giant cosmic structures and supermassive black holes were forming.”

Gavin Ramsay, Research Astronomer at AOP notes, “when I started my PhD at MSSL in 1991 I was given data obtained from the Rosat satellite, a UK/German/USA X-ray satellite launched in 1990. During the first 6 months it made an all-sky survey at soft X-ray energies after which it made a series of more detailed observations of bright X-ray sources. The new eRosita mission is a German/Russian X-ray satellite which has a long and complex history.”

Gavin continues, “the all-sky image seen above is a beautiful image in roughly the same energy range as Rosat, but with much greater sensitivity. What is still to come is the first all-sky image at much harder X-ray energies which Rosat wasn’t sensitive to. Rosat data was used to find two objects which were later found to be the most compact binary then (and still known). eRosita is sure to find a whole zoo of weird and interesting objects.”