# If the universe is expanding faster than light speed does that mean that stars can intercept/overtake light photons that they have previously emitted?

If parts of the universe are accelerating faster than the speed of light does that mean that stars can catch up with and overtake the light photons that they have previously emitted traveling in the same direction that they are being expanded in? Or is it that just the space between stars is being stretched to the effect that the light/photons they emit become trapped in that ever stretching space and can never escape or be overtaken by their own star? Also, if a star can intercept with its own photons what occurs when it collides with them?

On scales much smaller than the Hubble length $(c/H_0)\approx 4 Gpc$ one can use the Newtonian approximation for the expansion and define the expansion velocity as $v=H_0 d$, where $H_0$ is the Hubble constant, $d$ is the distance, and $c$ is the speed of light. It follows from these formulas that where this approximation can be used, $v\ll c$. For larger distances, general relativity is needed to model the expansion and relative velocity is not well defined for two separate spacetime points in general relativity. So it doesn't make sense to say "the universe is expanding faster than the speed of light". Therefore nothing can overtake light even in an expanding Universe.
• It should be pointed out that you can define apparent velocity due to expansion however, namely $v=H \Delta s$, where $H$ is the Hubble parameter and $\Delta s$ is their distance apart. – Jold Feb 18 '17 at 3:47