| quasar | violent galaxy | QSO | An object with a dominant starlike (i.e., diameter less than 1") component, with an emission line spectrum showing a large redshift - up to z = 3.53 (0.91c) for OQ 172. (The largest redshift known for a normal radio galaxy is z = 0.637 for 3C 123.) Many have multiple absorption redshifts; a few have multiple emission redshifts. (Bahcall system: class I, zabs ≈ zem; class II, zabs significantly less than zem.) The light of most if not all quasars is variable over time intervals between a few days and several years, so their diameters must not be much larger than the diameter of the solar system; yet they are the intrinsically brightest objects known (for 3C 273 (z = 0.158), Mv = -27.5 if its redshift is cosmological). The energy output of a typical quasar at "cosmological" distance is of the order of 1047 ergs per second - which would require a mass of 1010 Msun if it derives its energy solely from nuclear fusion. (Energy requirement under the "local" hypothesis is on the order of 1042 ergs per second.) The basic problem of quasars is that they emit too much radiation in too short a time from too small an area. |
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