Could the Earth be swallowed by a black hole?
Most black holes that we know of are at a safe distance. But there might be rogue black holes drifting through space, gobbling up matter as they go.
If the Sun were replaced by an equally massive black hole, all the planets would remain in their present orbits, circling the black hole at a safe distance. Life would be impossible without the light and heat from the Sun, but at least Earth would survive. However, if a black hole as massive as the Sun entered our Solar System by some other means, things would be quite different. Planets would be slung away into space by gravitational forces, or they would be ripped apart by the strong tidal forces of the black hole. But thankfully, the chances of this happening are very slim.
It's the nightmare of every science fiction hero: falling into a black hole. Luckily, there are no black holes in our cosmic neighbourhood, so there's no need to worry.