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Faint Blue Stars: In 1964, Allan R. Sandage of Mount Wilson and Palomar Observatories discovered distant objects that resemble quasars in all respects except that they lack strong radio emission; hence these have been called quasi-stellar galaxies (QSG). Years ago, all such objects were thought to be faint blue stars inside our own galaxy, as indeed most of them are. After quasars were identified, the true QSG's were called interlopers, to emphasize both their similarities to and differences from quasars.
History and Importance. The first quasars, then believed to be stars, were found in 1960 during optical identifications of bright radio sources listed in the Third Cambridge (3C) Catalogue of Radio Sources. Most of the 3C sources that have very small radio angular sizes proved to be quasars. Although it has often been difficult to pick out a quasar from a rich field of stars, recognition of their relatively blue colors has helped in the identifications. More than 50 quasars were known by the mid-1960's.
Astronomers immediately began to consider as sources two types of unusual stars in which very high densities were known to occur. In one type, the so-called white dwarfs, matter has been compressed to great densities. If the sun were made of such dense matter it would make a body only about as large as the earth. Because of their small size white dwarfs are very faint. Great numbers of them are believed to exist, but only the nearest ones can be seen. |
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