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View Full Version : Why are quasars redshifted?



chornedsnorkack
2012-Mar-20, 12:55 PM
They are said to emit from high-speed jets erupted towards us.

If so, why are they redshifted? Shouldn´t they be blueshifted because, although the source of the jet indeed recedes at a high speed, the matter in the jet, having been ejected at even higher speed, should be approaching?

ngc3314
2012-Mar-20, 01:08 PM
No, some quasars include emission from relativistic jets (radio-quiet ones either completely or substantially lack such components). And in jets from AGN, no discrete spectral features from which to measure a redshift are seen. (The jets of the microquasar SS433 are the only similar jets from which redshifts can be measured spectroscopically - we don't quite know how they manage to have clumps that are that coherent in velocity, but SS433 clearly knows). The prominent emission lines from active galaxies arise from much slower-moving gas around the core; some show evidence of kinematic Doppler shifts, but at most of a few thousand km/s seen in certain ionized species.