Will acceleration rate of expansion of space become faster than speed of light?

Question

From watching cosmology lectures, it seems that the space between galaxies is expanding at an accelerating rate, my question is since it is the space that is (acceleratingly expanding), the special relativity does not apply in this case? in other words since it is not anything that is accelerating with relative distance, would at some point galaxies that are far enough from each other separate faster than speed of light?

Please note, I am not asking if the galaxies would move faster than speed of light, but whether the rate of expansion of space be faster than speed of light so in effect each galaxy would be as if it is behind an event horizon where even light can not escape?

If yes, is there a name for such an even horizon that is cause by expanding space outside rather than the conventional black hole event horizon caused by stretching of space within the event horizon?

How would one be able to differentiate between a black hole even horizon and a galactic even horizon caused by accelerating expansion of space outside? (not sure if the concepts of inside and outside are still meaningful in such cases)

Answer 1

Yes indeed, in the circumstances you describe a horizon does form, and it's called a cosmological event horizon. Googling for this term will lots of articles on the subject, though for once Wikipedia has let me down and does not have a good article on the subject. However each galaxy wouldn't be behind it's own horizon as groups of galaxies tend to be gravitationally bound together. For example the Milky Way would stay bound to Andromeda and a dozen or so smaller galaxies.

Your question suggests you're think of this horizon as a sort of shell that would stop outsiders looking in on the galaxy behind the horizon, but it's really the other way round. The cosmological event horizon is like a shell that stops us looking out. In this respect it's the opposite of a black hole that stops us looking in.

A quick footnote: I had another Google and found http://www.mso.anu.edu.au/~charley/papers/DavisLineweaver04.pdf, which seems interesting reading on the subject.