Structural formation of the universe: As observed by X-ray satellites

Most celestial bodies emit their energy in the 0.5–5 keV range, thus the universe is very bright in X-rays. The Earth's atmosphere protects life on earth from being burned out by the high energy UV and X-ray, while blocking the precious information from the universe. Therefore, the X-ray satellites should be placed either at high altitudes in order to have a clear vision of stars, galaxies and unveil the cosmic mystery. According to structural formation hierarchy of the universe, stars form galaxies and galaxies form clusters. Galaxy clusters are the largest gravitational entities of the universe, and yet one of the brightest X-ray sources in the universe. In this paper, we review the large-scale structural formation of the universe based on the analysis results of our TUBITAK scientific research project on clusters of galaxies with X-ray data, which is obtained from the scientific satellites facing outer space such as NASA's Chandra, ESA's XMM-Newton and ISAS/JAXA's Suzaku.