It's a rare pleasure to announce that a new astronomical satellite is scanning the skies, but today is such a day: eROSITA is now orbiting the Sun and scanning the sky in X-rays!
eROSITA stands for extended ROentgen Survey with an Imaging Telescope Array. It's a collaboration between Russia and Germany (Wilhelm Röntgen, sometimes spelled Roentgen, discovered X-rays in 1895 and his patronymic was used as an old style unit of X-ray radiation), and is a survey telescope, designed to scan the entire sky over its nominal 7-year mission. It just had "first light", meaning its first observations, and those have now been released.
X-rays are emitted by high-energy events: exploding stars, extremely hot stars, black holes gobbling down matter, and so on. A big source of cosmic X-rays is gas that exists between galaxies in galaxy clusters. These clusters are the some of the largest coherent structures in the Universe, and were among the first things to form in the early Universe.
This makes them interesting bellwethers for cutting-edge physics. Gravity dominates their structure, and while some of the gravity between galaxies and clusters is due to normal mater, it's dominated by dark matter, the invisible stuff that we ...