... Credit: X-ray: NASA , CXC , INAF , S. Andreon et al. ... Since telescopes are therefore also time portals , observations of distant clusters can be used, for example, to investigate when and how these huge galaxy conglomerations formed. ... The hot X-ray gas that confirmed the apparent galaxy grouping as a true cluster of galaxies is shown above in diffuse blue, superposed on an optical image showing many foreground stars. ... NASA Official: Jay Norris. ... Publications with keywords: galaxy cluster...