K I Kellermann
Abstract.
Although the extragalactic nature of quasars was discussed as early
as 1960, it was rejected largely because of preconceived ideas about
what appeared to be an unrealistically high radio and optical
luminosity. Following the 1962 occultations of the strong radio
source 3C 273 at Parkes, and the subsequent identification with an
apparent stellar object, Maarten Schmidt recognized that the
relatively simple hydrogen line Balmer series spectrum implied a
redshift of 0.16. Successive radio and optical measurements quickly
led to the identification of other quasars with increasingly large
redshifts and the general, although for some decades not universal,
acceptance of quasars as being by far the most distant and the most
luminous objects in the Universe. Arguments for a more local
population continued for at least several decades, fueled in part by
a greater willingness to accept the unclear new physics needed to
interpret the large observed redshifts rather than the extreme
luminosities and energies implied by the cosmological interpretation
of the redshifts.
Curiously, 3C 273, which is one of the strongest extragalactic sources in the
sky, was first catalogued in 1959 and the magnitude 13 optical counterpart was
observed at least as early as 1887. Since 1960, much fainter optical counterparts
were being routinely identified using accurate radio interferometer positions,
measured primarily at the Caltech Owens Valley Radio Observatory. However, 3C
273 eluded identification until the series of lunar occultation observations
led by Cyril Hazard. Subsequent attempts to classify quasars into numerous
sub-categories based on their observed optical, radio, IR and high energy
properties have perhaps led to more confusion than clarity. However, quasars
and the broader class of AGN are now a fundamental part of astrophysics and
cosmology. They were the basis for the recognition of supermassive black holes
in galactic nuclei, which are intimately tied to the formation and evolution of
stars and galaxies.
Keywords: quasars: general -- quasars: emission lines -- radio continuum: stars --
galaxies: distances and redshifts -- galaxies: active -- occultations --
history and philosophy of astronomy
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