Just in case I haven't made the Universe scary for you yet: when a massive star undergoes core collapse, the material of the core falls inward at a rate of ONE QUARTER OF THE SPEED OF LIGHT (or, ~70,000 kilometers-per-second). What happens next depends on a few factors:
1. If the core is not /that/ massive (but really, it IS /that/ massive compared to our star), and degenerate (the electrons of it's matter is stacked in the same exact spot), it will collapse into a Neutron Star (pretty much a star composed purely of ions, electrons, and subatomic particles). These are freaky in their own right (one was found to adjust and release a TON of gamma rays back in 2004 about 50,000 light years from us; had it been ~10 light years away, almost everything on Earth would've died in a mass extinction), and a topic for another day (wait until I tell you what happens if two of these sexy things collide~).
2. If the core is /THAT/ massive and degenerate, it'll just straight-out collapse into non-existence (or, pure information), and become a black hole. These aren't really the murder-machines we think they are, because they're more impossible to feed than a rock. That alone is a topic for another day (if anyone wants to know what I mean, message me or something).
3. Finally, if the core isn't degenerate (electrons are NOT stacking up like cards), it collapses rapidly, with the outer layers of gases being blown out into its system. Then, the collapse causes what's left of the core to heat up so much and so fast that it IGNITES and explodes. So it pretty much turns into a huge firebomb, rapidly blowing out into its system and destroying everything in its path back down into dust and gas.
Also, I lied. There's a fourth thing that could happen: if the core is BIGGER than 130-times the mass of the Sun, its collapse becomes so hot, that instead of igniting the LIGHT causes photodisintegration to begin. This is where photons are SO energetic that they outright destroy matter. As a result, it gets so hot, that its hot disintegrates it and it becomes a black hole. (but don't worry, after it sucks in enough crap, it's near-impossible to feed, like I said earlier)
In the words of my astronomy professor: "The Universe is out to kill you." Pleasant dreams~~
