![]() This implies an extremely high power density. 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. The spectral lines of these objects, which identify the chemical elements of which the object is composed, were also extremely strange and 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. But when radio astronomy began in the 1950s, astronomers detected, among the galaxies, a small number of anomalous objects with properties that defied explanation. Main article: Galaxy § Distinction from other nebulaeīetween 19, it became clear from work by Heber Curtis, Ernst Öpik and others that some objects (" nebulae") seen by astronomers were in fact distant galaxies like the Milky Way. ![]() History of observation and interpretation For convenience, the abbreviated form "quasar" will be used throughout this paper. Because the nature of these objects is entirely unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name. So far, the clumsily long name "quasi-stellar radio sources" is used to describe these objects. The term "quasar" was first used in an article by astrophysicist Hong-Yee Chiu in May 1964, in Physics Today, to describe certain astronomically puzzling objects:
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