For all it's worth, there's no need to go black hole to explain the lack of visual observation. Objects that far from a star reflect very little if any light and would appear black to a black background.
> If a black hole with a mass of, say, Ceres hit the Earth, it would not be particularly worse than if Ceres hit the Earth.
This equivalency is true for many aspects of orbital mechanics (depending on setup giving sufficient distance), but I don't believe that's true at all for a collision. Someone with more knowledge correct me, but a black hole with the mass of Ceres would be very tiny but also emitting a ton of radiation. The collision would be very different.
I more mean that the resulting moon-sized fragments of what used to be the earth would be equally devoid of life. I agree the physics might vary somewhat.
If the black hole had a mass more similar to a 0.5-mile asteroid...well, I'm not sure what would happen. Would it just punch a hole straight through the earth?
Sort of. Ceres can't turn mass into energy at a ratio that makes fusion and fusion look pretty lame.
On the other hand taking 0.00016 of earths mass, turning it into a blackhole, and shooting it through the earth isn't likely to cause nearly the damage that Ceres (100x size of the dinosaur killing asteroid) ... unless you keep the velocity low enough that it stays inside the earth.
For all it's worth, there's no need to go black hole to explain the lack of visual observation. Objects that far from a star reflect very little if any light and would appear black to a black background.