Mathematics – Logic
Scientific paper
Mar 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984msngr..35...13c&link_type=abstract
The Messenger, No. 35, P.13, 1984
Mathematics
Logic
1
Scientific paper
The story of the discovery of quasars has been told many times (see e.g. the 24th Liege International Astrophysical Colloquium 1983), nevertheless, it is always exciting to recall the first uncertain steps taken around 1960, when very little was known about this major component of the universe. In that period the identification of several radio sources, listed in the 3C catalogue, with more or less distant galaxies had been performed, but for many of them the optical counterpart was still unknown. In 1960 Matthews et al. (1) investigated with the 200" telescope of Mt. Palomar the fields corresponding to the sources 3C48, 3C196 and 3C286. They could not find any trace of galaxies, the radio position indicating on the contrary three objects of stellar appearance. At that time no radio star was actually known besides the Sun, thus the discovery raised some questions, which became even more puzzling when spectroscopic observations revealed that each of these "stars" emitted a lot of ultraviolet and blue light with a few emission lines, different from case to case, which could not be plausibly identified with any known element. Many theoretical possibilities were opened, but, before any thorough examination could be performed, the nature of the problem was completely changed with the identification of the radio source 3C273, carried out by Hazard, MacKey and Shimmins in 1962 (2) with the 210ft Parkes radio telescope. By means of several lunar occultations, the position of the source was measured with an uncertainty less than 1" and its structure was shown to consist of two components separated by 19.5 arcsec. The relative accuracy of these measurements allowed an indisputable optical identification with a stellar object of about 13th V magnitude with an associated jet extending as far as 19.3 arcsec. Schmidt (3) took a spectrum of this object, which showed six broad emission lines which could be interpreted as being due to known elements assuming an unexpectedly large redshift of 0.158. It was possible to apply the same interpretation to 3C48, 3C196, and 3C286, when their spectra were reexamined, adopting respectively redshifts of 0.37, 0.87 and 0.85. At that time the radio galaxy 3C295 (z = 0.46) was already known, nevertheless the discovery was upsetting: if the redshift of 3C273 is cosmological, then its absolute magnitude is -27 (assuming a Hubble constant of 50 km/s/Mpc), that is about 40 times brighter than the brightest galaxies.
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