Superluminal speed? I came by the quotation below.
I'm confused: does it mean that it's actually possible for light and even material objects to move faster than light?

Gravitational fields are present the velocities of either material bodies or of light can assume any numerical value depending on the strength of the gravitational field. If one considers the rotating roundabout as being at rest, the centrifugal gravitational field assumes enormous values at large distances, and it is consistent with the theory of General Relativity for the velocities of distant bodies to exceed 3 × 10^8 m/sec under these conditions
(An Introduction to the Theory of Relativity, William Geraint Vaughn Rosser, 1964, p. 460. Rosser was the senior lecturer in Physics at Exeter University).

 A: In a rotating reference frame, the coordinate velocity of an object can exceed $c$.  However, this doesn't mean that they're moving "faster than light".  If we were to look at the light-cones at these distant locations, we would see that the four-velocities of these objects are still confined within the light-cones at those locations.  To put this another way, if I was sitting on a roundabout and watched a distant object emit a pulse of light in all directions, I would observe an expanding "shell of light" around the object.  The object would never be able to outrun the light pulse in any direction, and so would remain inside this "shell" for all time.  This does imply that the photons emitted in the forward direction would have a coordinate velocity even greater than $c$, but that's not really a problem.
This phenomenon is much more common in general relativity, where coordinate velocity (i.e. rate of change of spatial coordinate $x$ with respect to time coordinate $t$) doesn't really have any innate meaning because the coordinates we set down on spacetime are largely arbitrary.  A good example of this is the Alcubierre "warp drive" spacetime, where an object's coordinate velocity can be much greater than $c$, but which is still traveling (locally) slower than the speed of light.
