3C273 Image

HST image of 3C 273. Note the starlike
appearance. Note also the jet of material being ejected toward the lower right.

In the late 1950s radio astronomers began compiling catalogs of radio sources. At that time there were quite a number of radio
sources which were not associated with previously known optical objects. The primary difficulty was that radio telescopes had poor
resolution and large beam sizes so that it was often not possible to identify which of as many as several hundred faint stars was
actually associated with a strong radio source. (Note that today this would not be a problem due to the advancements in resolution
brought about by radio interferometric techniques). In 1960 one unassociated radio source (3C
48) was finally identified with a 16th magnitude stellar object. The identification was made when the moon occulted the radio
source. Since this relatively strong radio source was associated with an object that appeared stellar, this category of objects became
known as quasi-stellar radio sources (QSRS). This is the origin of the name quasar.
3C 273 Spectrum

Discovery spectrum of 3C 273. Note the redshift of the hydrogen lines in the source relative to the
comparison spectrum. The wavelengths of H-Delta, H-Gamma and H-Beta are, respectively, 410, 434 and 486 nm.

When Maarten Schmidt measured the spectrum of 3C 273 in 1964 it was the most distant object known… for about 15 minutes! Then his
colleagues in the next office measured the spectrum of 3C 48, which gave z = 0.36.

When a spectrum of this faint source was obtained it was observed to have strong broad emission lines which could not be
identified with emission lines of known chemical elements. In 1963 the strong radio source 3C 273 was also identified with an
inconspicuous 13th magnitude “star.” This object too exhibited strong emission lines which could not be
identified. Eventually a sequence of emission lines similar to the Balmer series of hydrogen was recognized in the spectrum of
3C 273, but shifted far to the red. The red shift observed for 3C 273, z = 0.158, was greater than the highest known
redshift for a galaxy. However, assuming this redshift, the remaining emission lines could readily be identified with the
standard emission lines known. Because the emission lines identified in this way are the same lines known to be present
in nearby galaxies, and because galaxies are the only objects known to have systematic large redshifts, quasars are
generally believed to be extragalactic.
If quasars are assumed to follow the Hubble law for distances, the the large redshifts must correspond with large distances.
Indeed, at the large distances implied by some quasar redshifts, a normal galaxy would be too faint to be observed. Thus, quasars would
appear to be hundreds of times brighter than normal galaxies.Quasars have now been observed with redshifts ranging from 0.06 to above 6.0. However, there are no nearby quasars, and the number of
quasars increases with redshift. Since redshift is related to distance, objects with large redshifts are farther from us; it has taken
their light longer to reach us, and so we see them from a time farther into the past. Since quasars are more numerous at high
redshift, they must also have been more common when the universe was younger. Quasars have either disappeared during the present time
or have changed their characteristics and evolved into less luminous objects. According to current thinking on the subject, all large
galaxies went through an active “quasar” stage early in their existence, but have now settled down into quiet middle age. In support
of this idea is the growing evidence that all large galaxies contain supermassive black holes at their cores… the
same type of object thought to power quasars and other AGN.


000-017   000-080   000-089   000-104   000-105   000-106   070-461   100-101   100-105  , 100-105  , 101   101-400   102-400   1V0-601   1Y0-201   1Z0-051   1Z0-060   1Z0-061   1Z0-144   1z0-434   1Z0-803   1Z0-804   1z0-808   200-101   200-120   200-125  , 200-125  , 200-310   200-355   210-060   210-065   210-260   220-801   220-802   220-901   220-902   2V0-620   2V0-621   2V0-621D   300-070   300-075   300-101   300-115   300-135   3002   300-206   300-208   300-209   300-320   350-001   350-018   350-029   350-030   350-050   350-060   350-080   352-001   400-051   400-101   400-201   500-260   640-692   640-911   640-916   642-732   642-999   700-501   70-177   70-178   70-243   70-246   70-270   70-346   70-347   70-410   70-411   70-412   70-413   70-417   70-461   70-462   70-463   70-480   70-483   70-486   70-487   70-488   70-532   70-533   70-534   70-980   74-678   810-403   9A0-385   9L0-012   9L0-066   ADM-201   AWS-SYSOPS   C_TFIN52_66   c2010-652   c2010-657   CAP   CAS-002   CCA-500   CISM   CISSP   CRISC   EX200   EX300   HP0-S42   ICBB   ICGB   ITILFND   JK0-022   JN0-102   JN0-360   LX0-103   LX0-104   M70-101   MB2-704   MB2-707   MB5-705   MB6-703   N10-006   NS0-157   NSE4   OG0-091   OG0-093   PEGACPBA71V1   PMP   PR000041   SSCP   SY0-401   VCP550   100-101   70-412   VCP550   LX0-104   000-017   70-461   700-501   70-347   EX200   SSCP   200-120   VCP550   NS0-157   400-201   N10-006   000-080   000-080   70-346   3002   300-101   PMP   640-692   ITILFND   ICBB   70-246   9L0-066