Superluminal jets

So I've skimmed certain papers several years ago indicating that radio jets and other accretion-related emissions from black holes can be superluminal.

Is this true, or is this just the relative motion of particles in some medium other than vacuum that exceeds the speed of light?

I'm assuming that detecting these involves detecting cherenkov radiation?

Sorry if this seems somewhat newbish, I'm hoping someone with more expertise in the field can shed some light on this. Thanks
 

mgb_phys

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No superluminal jets are an angle of view effect, nothing is travelling faster than light
This animation sort of explains it http://www.physics.purdue.edu/MOJAVE/superluminal.swf

Another way is the 'lighthouse paradox' imagine a powerfull jet of radiation on earth - say a laser beam, being spun around at a high rpm. You see the laser beam light up a dot that moves rapily across the surface of the moon - you measure the time taken to cross the moon and it works out at faster than c. But nothing is really moving 'across the moon' it's just the point where the beam hits something that lights up.
 
Ah! Now THAT makes sense! Thanks for the clarification, I'm glad to know the universe will be alright and we're not all going insane.
 

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