Yes, it's kind of feasible, theoretically speaking, not of course with a 'knife', but if you had a big enough blow torch. Obviously, it would have to be VERY BIG, in fact off the top of my head I'd calculate at over 1 light year in length (gives a new meaning to a 'light saber', LOL!).
Of course, we don't yet have the kind of meta-materials that could build such a crazy device, but I'm guessing a phase 3 Kardishian civilization would find it child's play.
In fact, there's speculation from some scientists that so called 'solar flares' are in fact an alien species doing this very thing, and probably blowing the fragments of the sun they have cut off to the outer solar system in order to heat up their worlds beyond the Oort clouds.