Quasars or quasi-stellar radio source are sources of electromagnetic energy which are characterized with high red shifts, thus leading scientists to conclude that not only they are moving away but are also at a great distance from us. Of the over 100,000 quasars identified to-date, the greatest proportion are over one billion light-years away (the closest quasar identified to-date is 780 million light-years away whereas the most distant quasar discovered so far is 13 billion light-years away). As a result, quasars represent entities from the universe's distant past.

Given their visibility (generally as point sources of light), it follows they must be associated with tremendous amounts of energy which is only exceeded in intensity by supernovae and gamma-ray bursts. Some examples of quasars also involve the centers of (active) galaxies and which has led to the suggestion that supermassive black holes at the galaxy center and the consequent accretion of material must fuel these quasars. The rapid change in luminosity observed for some quasars also suggests they must be relatively small entities.

Note: Markarian 205 in Draco is popular due to a slight controversy that has been generated surrounding its possible association with the dim galaxy NGC 4319 (mag 12.1) in the immediate area. It is now accepted that the disconcordant redshifts between Mrk 205 (z=0.07) and NGC 4319 (z=0.006) are a clear indication of the independence of these two objects and in spite of the suggestion (notably by Halton Arp) that Mrk 205 may be a quasar which has been ejected from NGC 4319. The pairing between Mrk 205 and NGC 4319 is simply an optical illusion (similar to optical double stars) where both Mrk 205 and NGC 4319 are in our line of sight with Mrk 205 being at a much greater distance from us than the intervening galaxy. Arp's contention of a physical relationship includes a Mt Palomar photo supposedly documenting a jet stream between NGC 4319 and Mrk 205 (see here) and which he uses to support his notion that these two entities are indeed related. The established computed distances for NGC 4319 (107 million light-years) and Mrk 205 (1.2 billion light-years) suggest otherwise.

Mrk 205 is located between Giausar (λ-Draconis, mag 3.81) and Kochab (β-UMi, mag 2.05) and is associated with a redshift of z=0.07 which suggests that it is receeding away from us at 6.8% the speed of light (ie. 20,250 km/sec). For the sake of completeness, NGC 4319 is associated with a reshift of z=0.006 (0.6% the speed of light).

Note: Halton Arp's case on the physical association between NGC 4319 and Mrk 205 is available here.