If you envisage a light pulse in a wave guide (glass tube) moving across an observers field of view, the pulse can only move at 'c' through the guide. The model identifies a difference between the information carried by the wave at its signal velocity 'c', and the information about the wave fronts apparent rate of change of position. Suggestions of turbulence and/or "wide cones" in the inner parts of the jets have been put forward to try to counter such problems, and there seems to be some evidence for this. The same group of scientists later revised that finding and argue in favour of a superluminal bulk movement in which the jet is embedded. But evidence suggests that the jet is in fact at about 43° to our line-of-sight. To explain this in terms of the "narrow-angle" model, the jet must be no more than 19° from our line-of-sight. Superluminal motion of up to 6c has been observed in the inner parts of the jet of M87.
Superluminal motion of up to ~9.6c has been observed along the (inner) jet of this quasar. suggested that the (outer) jet of the quasar 3C 273 is nearly collinear to our line-of-sight. (Their apparent length would appear much shorter if they were.) In other words the jets are evidently not, on average, close to our line-of-sight.
An embarrassment is that the average projected size of the outer structure is no smaller than that of the normal radio-source population. have revealed outer double structure in all but one ( 3C 273) of the known superluminal sources. Some contrary evidenceĪs early as 1983, at the "superluminal workshop" held at Jodrell Bank, referring to the seven then-known superluminal jets, If Doppler shifts are observed in both sources, the velocity and the distance can be determined independently of other observations. Superluminal motion is often seen in two opposing jets, one moving away and one toward Earth. This explanation depends on the jet making a sufficiently narrow angle with the observer's line-of-sight to explain the degree of superluminal motion seen in a particular case. This causes the light emitted over hundreds of years of travel to not have hundreds of lightyears of distance between it, the light thus arrives at the observer over a much smaller time period (ten or twenty years) giving the illusion of faster than light travel. To be more clear, the jet is essentially "chasing" the light it emits. Because at every point of their path the high-velocity jets are emitting light, the light they emit does not approach the observer much more quickly than the jet itself. This phenomenon is caused because the jets are travelling very near the speed of light and at a very small angle towards the observer. 2 Derivation of the relativistic explanation.
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