Editing Quasar (section)

=== Background ===
{{Main|Galaxy#Distinction from other nebulae}}

Between 1917 and 1922, it became clear from work by [[Heber Doust Curtis]], [[Ernst Öpik]] and others that some objects ("[[nebula]]e") seen by astronomers were in fact distant [[galaxies]] like the Milky Way. But when [[radio astronomy]] began in the 1950s, astronomers detected, among the galaxies, a small number of anomalous objects with properties that defied explanation.

The objects emitted large amounts of radiation of many frequencies, but no source could be located optically, or in some cases only a faint and [[point-like]] object somewhat like a distant [[star]]. The [[spectral line]]s of these objects, which identify the [[chemical element]]s of which the object is composed, were also extremely strange and defied explanation. Some of them changed their [[luminosity]] very rapidly in the optical range and even more rapidly in the X-ray range, suggesting an upper limit on their size, perhaps no larger than the [[Solar System]].<ref>{{cite web|url=https://hubblesite.org/contents/news-releases/1996/news-1996-35.html |title=Hubble Surveys the "Homes" of Quasars |publisher=HubbleSite |date=1996-11-19 |access-date=2011-07-01}}</ref> This implies an extremely high [[power density]].<ref>{{cite web |url=http://neutrino.aquaphoenix.com/un-esa/astrophysics/astro-chapter7.html |title=7. HIGH-ENERGY ASTROPHYSICS ELECTROMAGNETIC RADIATION |publisher=Neutrino.aquaphoenix.com |access-date=2011-07-01 |archive-url=https://web.archive.org/web/20110707154332/http://neutrino.aquaphoenix.com/un-esa/astrophysics/astro-chapter7.html |archive-date=2011-07-07 |url-status=dead }}</ref> Considerable discussion took place over what these objects might be. They were described as ''"quasi-stellar'' [meaning: star-like] ''radio sources"'', or ''"quasi-stellar objects"'' (QSOs), a name which reflected their unknown nature, and this became shortened to "quasar".