What is the speed of gravity and its relationship to light?

[OwenMc]

Having read the recent thread on gravity waves, I was intrigued by the question of speed. This question has always bothered me when thinking about gravity, although this is probably because I'm not much of a physicist!
Firstly, the speed of gravity, as discussed in the previous thread. If the sun did vanish, would we continue to orbit it for 8 minutes? Or, if gravity is "instantaneous" would we shoot off in a straight line immediately despite still being able to see the sun for a further 8 minutes?
Secondly, assuming gravity propagates at the speed of light, this does suggest some kind of symmetry between light and gravity as Quasar2287 suggested in the previous thread. If so, does that mean all massive objects "emit" gravity? in the same way that all radiative objects "emit" photons?
I'm confusing myself as I write this, so I'll throw open the floor to your comments!

 

[mgb_phys]

Gravity doesn't travel - it's a property of space time.
Changes in gravity (such as the sun dissapearing) travel at the spee dof light, otherwise you could use a moving mass to send messages faster than light.
This is a fundamental principle of relativity - it doesn't really matter what your model for gravity is (gravitons, strings etc).

 

[Chronos]

Google on Gravity Probe B for confirmation of General Relativity predictions.