The dominant luminous component in a cluster of galaxies is the 10 to 10 kelvin intracluster medium. The emission from the intracluster medium is characterized by thermal bremsstrahlung. This radiation is in the energy range of X-rays and can be easily observed with space-based telescopes such as Chandra X-ray Observatory, XMM-Newton, ROSAT, ASCA, EXOSAT, Suzaku, RHESSI and future missions like IXO [https://web.archive.org/web/20080303062108/http://constellation.gsfc.nasa.gov/] and Astro-H [https://web.archive.org/web/20071112015825/http://www.astro.isas.ac.jp/future/NeXT/].
Bremsstrahlung is also the dominant emission mechanism for H II regions at radio wavelengths.