Quasars are very high redshift (figure 1) astronomical objects with broad emission line (BEL) spectra. The latter is very different to that in the usual ‘normal’ galaxies. This means the objects’ redshifts and BEL spectra can be used to identify them.
And because of their high redshifts they are assumed to be very distant, very luminous active galaxies with super-massive black holes at their hearts, powering them to emit prodigious amounts of radiation over all wavebands of the electromagnetic spectrum.
Most of the high redshift objects in the universe are quasars. The redshifts of galaxies and quasars when interpreted within big bang cosmology—the greater the redshift the greater the distance—means that the most distant objects are seen at a time when the universe was youngest.1
Following big bang thinking, quasars are then considered to be just galaxies in some early stage of development—back closer in time to the big bang—than the usual spiral and elliptical galaxies we might see with much lower redshifts.
The quasar 3C 273, shown in figure 2, the first to be identified (discovered in the early 1960s by astronomer Allan Sandage), has been shown to reside in a giant elliptical galaxy in the constellation of Virgo. According to standard cosmology, its redshift puts it at a distance of 2.5 billion light years from Earth.
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