Star Trek (2009)

Movie

Among massive pyrotechnic displays, the Romulans drill a hole into the core of the planet Vulcan, drop in some magic "red matter," and the planet is suddenly transformed into a planet-size black hole. Later, Spock returns the favor, sprinkling red matter into a Romulan ship that collapses to form its own black hole.

The Science

Even for a technologically advanced society like the Romulans, it's not possible to create a black hole by just dropping some unnamed form of matter in the middle of a planet (or a starship). (And how would you contain the mysterious "red" matter without having it turn whatever surrounds it into a black hole?) The only way to do it would be to crush the existing planet to infinite density, which would make it about the size of a ball bearing, not the size of a planet. And the laws of physics would be fighting you all the way, heating the infalling material and blowing it back out instead of allowing it to plunge into the black hole. There's a reason you need the mass and gravitational pull of a supermassive star to create a black hole!