Astronomers used a space telescope called eROSITA to map half of the universe in X-rays. The new map contains nearly a million X-ray sources and is the basis for dozens of new scientific papers, with more to be published soon.

eROSITA map seen in two different ways: left showing extended X-ray radiation, right showing point X-ray sources

eROSITA is a soft X-ray imaging telescope located at Lagrange Point 2, a neighbor of the James Webb Space Telescope. The goal is to scan the entire sky using X-ray wavelengths to detect new galaxies, galaxy clusters, supermassive black holes and other celestial objects, study massive structures, and help measure dark energy - the mysterious force accelerating the expansion of the universe.

The first official data released is called the eROSITA All-Sky Survey Catalog (eRASS1) and is constructed from data collected by the telescope between December 12, 2019, and June 11, 2020. During this time, eROSITA was able to capture 170 million individual X-ray photons, allowing detailed maps of the universe to be created by measuring the energy and arrival time of each photon.

In this case, the map covers half of the night sky - the Western Hemisphere - and contains more than 900,000 X-ray sources. These include approximately 710,000 supermassive black holes that devour matter at the centers of galaxies, 180,000 X-ray-emitting stars in the Milky Way, 12,000 galaxy clusters, and some less common objects such as pulsars, supernova remnants, binary stars, and other X-ray sources.

Andrea Merloni, principal investigator of eROSITA, said: "For X-ray astronomy, these numbers are astounding. We have detected more sources in six months than the large flagship missions XMM-Newton and Chandra have detected in almost 25 years of operation."

At the same time as the first large-scale public release of data, nearly 50 new papers were also published based on eRASS1. These include the discovery of more than 1,000 superclusters of galaxies and the 42 million light-year filaments of gas that connect two galaxy clusters, how a star's X-ray radiation affects the habitability of its planets, and the study of X-rays from supernova remnants, stars and other celestial bodies.

eROSITA scanned the skies three more times between June 2020 and February 2022, when the joint German-Russian project was put on hold due to Russia's invasion of Ukraine. Data from these scans will be released in the near future.

All scientific publications based on these data can be found on the eROSITA website.