Editing Einstein Observatory (section)

===X-ray background===
Surveys by early x-ray astronomy experiments showed a [[X-ray background|uniform diffuse background of x-ray radiation]] across the sky. The uniformity of this background radiation indicated that it originated outside of the [[Milky Way Galaxy]], with the most popular hypotheses being a hot gas spread uniformly throughout space, or numerous distant point sources of x-rays (such as [[quasar]]s) that appear to blend together due to their great distance. Observations with Einstein showed that a large portion of this x-ray background originated from distant point sources, and observations with later x-ray experiments have confirmed and refined this conclusion.{{sfn |Tucker |Tucker |1986 |p=93-95}}