Sort of like a lens since the gravitational effect of matter converges timelike and null curves.
You might want to lookup the Raychaudhuri equation, it shows how nearby curves relate to each other in terms of expansion. You also might want to look up vorticity and shear in this context.
Thats a very interesting question.
It can definitely act as a lens (see gravitational lensing).
And i haven't heard about it before explicitly, but thinking about it - you would have a diffraction gradient effect because higher energy light would be less deflected than lower energy light. Can anyone back this up? (or counter it?)