How were quasars first discovered in radio surveys of the 1950s?
Shown are apparently normal, solitary galaxies (left), colliding galaxies (centre), and merging galaxies (right).
In the 1950s, astronomers conducting early radio surveys of the sky identified various radio sources away from the plane of the Milky Way Galaxy. While most of these sources were associated with normal-looking galaxies, some coincided with objects that appeared to be unusually blue stars.1
Because these objects possessed an almost starlike appearance, they were dubbed "quasi-stellar radio sources," a term that was shortened to "quasar" by 1964. Although they appeared starlike, photographs of some of these objects revealed they were embedded in faint, fuzzy halos. The true nature of these objects remained a mystery until 1963, when Maarten Schmidt determined that their unusual emission line spectra were caused by high redshift, indicating they were located at immense distances.1