In the 1990s, scientists detected that the universe was actually accelerating in its expansion rather than decelerating due to gravity. Why this is occurring is not well understood. It is believed that dark energy may be behind the accelerating expansion of the universe. It is believed that this dark energy makes up about 68% of the universe, dark matter makes up 27% of the universe, and everything else in the universe which can be seen by our telescopes(galaxies, stars, planets, etc) make up about 5% of the universe.

The German X-ray telescope, eROSITA, was set to launch on June 22, 2019, and will launch from the Baikonur Cosmodrome, a former Soviet launch complex located in current day Kazakhstan. The telescope will be launched along with a parent satellite called Spektr-RG.

The eROSITA will mainly examine galaxy clusters for its search for dark energy because they could emit X-rays that can then allow the telescope to track how the galaxy clusters move as well as how fast they are traveling. The telescope will also examine the gas from supernovas, neutron stars, as well as the nuclei of the galaxies that contain black holes in their centers. eROSITA will map the X-ray emissions coming from all over the universe and will create a large set of data on the objects described above and will improve our understanding of the universe.