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The Universe S04 E10 - Pulsars & Quasars - video dailymotion
They are point-like, similar to stars , rather than extended sources of light, such as galaxies. Although there was some initial controversy over the nature of these objects, the current scientific consensus is that a quasar is a compact halo of matter surrounding the central supermassive black hole of a young galaxy. Quasars display a very high redshift, indicating that quasars and the Earth are rapidly moving away from one another, as part of the process of the expansion of the universe.
When combined with Hubble's law, the implication is that quasars are very distant. To be observable at that distance, the energy output of quasars must dwarf that of almost every known astrophysical phenomenon in a galaxy, except for comparatively short-lived events like supernovae and gamma-ray bursts.
Quasars may readily release energy in levels equal to the output of hundreds of average galaxies combined. The output of light is equivalent to one trillion Suns. In optical telescopes, quasars look like single points of light i.
The galaxies themselves are often too dim to be seen with all but the largest telescopes. Most quasars cannot be seen with small telescopes, but 3C , with an average apparent magnitude of At a distance of 2. The highest redshift currently known for a quasar is 6.
Quasars are believed to be powered by accretion of material into supermassive black holes in the nuclei of distant galaxies, making these luminous versions of the general class of objects known as active galaxies. No other currently known mechanism appears able to explain the vast energy output and rapid variability. Knowledge of quasars is advancing rapidly.
As recently as the s, there was no clear consensus as to their origin. The first quasars were discovered with radio telescopes in the late s.
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Many were recorded as radio sources with no corresponding visible object. Using small telescopes and the Lovell Telescope as an interferometer, they were shown to have a very small angular size. In , radio source 3C 48 was finally tied to an optical object. Astronomers detected what appeared to be a faint blue star at the location of the radio source and obtained its spectrum. Containing many unknown broad emission lines, the anomalous spectrum defied interpretation—a claim by John Bolton of a large redshift was not generally accepted.
In , a breakthrough was achieved. Another radio source, 3C , was predicted to undergo five occultations by the moon. Measurements taken by Cyril Hazard and John Bolton during one of the occultations using the Parkes Radio Telescope allowed Maarten Schmidt to optically identify the object and obtain an optical spectrum using the inch Hale Telescope on Mount Palomar. This spectrum revealed the same strange emission lines.