Close its mouth at the speed of light?
Close its mouth at the speed of sound?
Close its mouth faster than the speed of light?
Also… wouldn’t it be heavier than the galaxy itself? So it would create its own gravitational pull that’s like extremely strong?
Man, I'm disappointed.
Of course this could exist!
And it would close its mouth as fast as a snapping turtle can, but at scale. That sucker would cause a gravitic ripple as its mighty jaws go so much faster than the speed of light that it creates hyperphotons that ricochet back and forth off of the current boundaries of the universe.
It can do this because it is a non-physical entity from the higher dimensions where time is considered passe, and only suitable for microentities that have no conception of true sapience, yet claim to be the highest intelligence around.
Simply put, this is nothing more than a shadow of the shadow of a multi-dimensional being that dwarfs gods. It devouring the galaxy is akin to breathing for us.
Look, nobody said we had to limit ourselves to science fact.