Quasar Light Journey Figure
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Quasar Light Journey

Artist impression of the quasar light in its journey from the source to the telescope
The distances to the quasars are so great that, even at the speed of light, photons have travelled for a significant proportion of the age of the universe before reaching the Earth. In its journey from the quasar to our telescopes, the emitted light passes through intervening material randomly distributed along the line of sight. This matter is too distant to be seen directly, but leaves its signature in the qusar spectrum in the form of narrow, discrete absorption lines. Thus quasar are veritable 'cosmic beacons', offering us a unique view of the universe as it was at much earlier times. At least two different types of absorbing regions produce absorption lines: haloes of galaxies where the interstellar medium is broadly similar to our own, and intergalactic clouds of primordial gas, which has undergone little or no metal-enrichment through stellar nucleosynthesis.  [ TIFF ]

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Last modified: 13 December 2010