It's plain javascript. I used canvas and reflected the coordinates of pixels according to position of cursor. Also smoothed the effect using a heuristic smootherstep function.
At present, the title here on HN is "Gravitational lensing by spinning black holes in astrophysics" -- to which my immediate reaction, and I suspect not only mine, is: what, as opposed to in cookery?
The original article title gives the answer: "... and in the movie Interstellar". Since the article really is about the rendering techniques used in the movie as well as about the physics of rotating black holes, I suggest that the HN title be made to match that of the original article.
I saw the title and thought "is it the one from Interstellar!?!?"
Thorne said he was going to publish based on their simulations so it's awesome it's here. I agree it might be nice to have the context in the title since this is cool for both physics and science-fiction fans.
http://cihadturhan.com/lab/gravitional-lensing/