Strangelets are tiny ‘fun-sized’ nuggets of strange-quarks (not to be confused with the regular, or familiar-quarks). Thought to be a by product of the Big Bang, scientists have been unable to detect their presence, until now.
Not quite the same scale as a wandering black hole swallowing the Earth, but still cool.
Off the top of my head, SF books about Earth and Black Holes:
Forge of God, Greg Bear
Singularity, Bill DeSmedt (a favorite of SFSignal)